Papers - TAKEMOTO Yoshito

Structural Changes due to Heating and Stress Loading of Metastable Quenched Martensite Structures in Ti-(10-20) mass％ Nb Alloys Reviewed

Yoshikazu Mantani, Yoshito Takemoto

Journal of the Japan Institute of Metals and Materials   88 ( 12 )   324 - 330   2024.12

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Japan Institute of Metals  

DOI： 10.2320/jinstmet.jc202407

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Reverse Shape Memory Effect and Toughness Recovery of Ti-10V-2Fe-3Al Alloy Reviewed

Yoshito Takemoto, Daiki Shinomiya, Taiki Ishihara, Hiroto Yokota, Jinta Arakawa

Journal of the Japan Institute of Metals and Materials   88 ( 10 )   239 - 244   2024.10

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Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：Japan Institute of Metals  

DOI： 10.2320/jinstmet.j202403

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Crystal plasticity analysis of fatigue crack initiation site considering crystallographic orientation in Ti–22V–4Al alloy Reviewed

Jinta Arakawa, Koki Hirazumi, Takeshi Uemori, Yoshito Takemoto

23   2024.9

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Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.rineng.2024.102405

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Elucidation of small fatigue crack initiation and propagation behavior on polycrystal Ti-22V-4Al Reviewed

Jinta Arakawa, Koki Hirazumi, Takeshi Uemori, Yoshito Takemoto

Procedia Structural Integrity   66   38 - 48   2024.9

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.prostr.2024.11.053.

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Testing Method and Design Guideline of Unit Cell Shape of Cellular Structures Made of AZ31 Magnesium Alloy Considering Application to Coronary Stent Reviewed

Ichiro SHIMIZU, Shunpei UEDA, Akira WADA, Tomoya KAGOTANI, Yoshito TAKEMOTO

Advanced Experimental Mechanics   2024.6

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Authorship：Last author  

DOI： 10.11395/aem.24-0007

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Microstructure and Shape Evolution in Ti-10V-2Fe-3Al Alloy by Tempering Invited Reviewed

TITANIUM JAPAN   71 ( 3 )   204 - 207   2023.7

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Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

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Study on joint characteristics in laser butt welding of AMed and wrought Ti6Al4V plates Reviewed

Yasuhiro Okamoto, Togo Shinonaga, Yoshito Takemoto, Akira Okada, Akihiro Ochi, Ryuya Kishimoto, Sisa Pityana, Nana Arthur, Peter Omoniyi, Rasheedat Mahamood, Martin Maina, Esther Akinlabi

Welding in the World   2023.6

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

Titanium alloy Ti6Al4V has been widely applied to medical, automotive, and aerospace industries due to its excellent properties such as high strength and excellent corrosion resistance. On the other hand, additive manufacturing (AM) technology can give the freedom of design of the products. In order to spread the AMed products, the joining of AMed and wrought products are required, and it is important to understand the joint characteristics. In this study, butt welding of Ti6Al4V plate was conducted by fiber laser in argon shielding, and the joint characteristics of laser weld wrought/wrought, AMed/AMed, and AMed/wrought Ti6Al4V plates were experimentally investigated. The AMed plate has higher tensile strength than wrought plate but the elongation of AMed plate is smaller, since AMed plate has α’ martensite due to rapid cooling during laser irradiation in AM process. Then, the laser weld joint of AMed/AMed plates has higher tensile strength, but smaller elongation than that of wrought/wrought plates. The weld joint of AMed/wrought plates shows good welding state, since small heat input leads to formation of small weld bead with higher hardness between wrought and AMed plates.

DOI： 10.1007/s40194-023-01533-3

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Other Link： https://link.springer.com/article/10.1007/s40194-023-01533-3/fulltext.html

Self-organized vertical multilayer structures in spinodally decomposed TiO2-VO2 films on glass substrates Reviewed

Yuji Muraoka, Kazutada Takeda, Yoshito Takemoto, Takanori Wakita, Takayoshi Yokoya

Thin Solid Films   769   139749 - 139749   2023.3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.tsf.2023.139749

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Structural Changes due to Heating and Stress Loading of Metastable Quenched Martensite Structures in Ti–(10–20) mass% Nb Alloys Reviewed

Yoshikazu Mantani, Yoshito Takemoto

MATERIALS TRANSACTIONS   64 ( 1 )   78 - 85   2023.1

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2320/matertrans.MT-MLA2022014

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Alloy Composition Dependency of Uniaxial and Biaxial Compressive Behavior of Metastable β-Type Titanium 10-18 mass% Molybdenum Alloys

Ichiro SHIMIZU and Yoshito TAKEMOTO

Advanced Experimental Mechanics   7   65 - 70   2022.8

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Language：English  

Alloy Composition Dependency of Uniaxial and Biaxial Compressive Behavior of Metastable β-Type Titanium 10-18 mass% Molybdenum Alloys Reviewed

Ichiro SHIMIZU, Yoshito TAKEMOTO

Advanced Experimental Mechanics   7   65 - 70   2022.8

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Formation Mechanism of Tempering-Induced Martensite in Ti–10Mo–7Al Alloy Reviewed

Yoshito Takemoto, Mikiko Yasuno, Masaki Ikemoto, Hiroyuki Ando, Ichiro Shimizu

MATERIALS TRANSACTIONS   63 ( 4 )   489 - 496   2022.4

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Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：Japan Institute of Metals  

DOI： 10.2320/matertrans.mt-m2021214

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Strain relaxation and spinodal decomposition in composition adjusted TiO2-VO2 films on TiO2(100) substrates Reviewed

Takahiro Fukuda, Yoshito Takemoto, Takanori Wakita, Takayoshi Yokoya, Yuji Muraoka

Thin Solid Films   751   139210   2022.4

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.tsf.2022.139210

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Effects of Thermomechanical Processing on Hydrogen Embrittlement Properties of UltraHigh-Strength TRIP-Aided Bainitic Ferrite Steels Reviewed

Tomohiko Hojo, Yutao Zhou, Junya Kobayashi, Koh-ichi Sugimoto, Yoshito Takemoto, Akihiko Nagasaka, Motomichi Koyama, Saya Ajito, Eiji Akiyama

Metals   12 ( 2 )   269 - 269   2022.1

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Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

The effects of thermomechanical processing on the microstructure and hydrogen embrittlement properties of ultrahigh-strength, low-alloy, transformation-induced plasticity (TRIP)-aided bainitic ferrite (TBF) steels were investigated to apply to automobile forging parts such as engine and drivetrain parts. The hydrogen embrittlement properties were evaluated by conducting conventional tensile tests after hydrogen charging and constant load four-point bending tests with hydrogen charging. The 0.4 mass%C-TBF steel achieved refinement of the microstructure, improved retained austenite characteristics, and strengthening, owing to thermomechanical processing. This might be attributed to dynamic and static recrystallizations during thermomechanical processing in TBF steels. Moreover, the hydrogen embrittlement resistances were improved by the thermomechanical processing in TBF steels. This might be caused by the refinement of the microstructure, an increase in the stability of the retained austenite, and low hydrogen absorption of the thermomechanically processed TBF steels.

DOI： 10.3390/met12020269

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Ti–10Mo–7Al合金の焼戻し誘起マルテンサイトの形成機構 Reviewed

竹元嘉利, 安野実希子, 池本雅基, 安藤寛幸, 清水一郎

日本金属学会誌   85 ( 11 )   405 - 412   2021.11

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Extremely Rapid Age Hardening in Ti-5Al-2Fe-3Mo Solution Treated at High α + β Temperature Region Reviewed

Tomonori Kunieda, Yusuke Kohigashi, Hideki Fujii, Kazuhiro Takahashi, Yoshito Takemoto

Metallurgical and Materials Transactions A   52 ( 10 )   4424 - 4437   2021.10

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s11661-021-06395-2

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Other Link： https://link.springer.com/article/10.1007/s11661-021-06395-2/fulltext.html

Effects of Matrix Structure and Nitrogen Content on Fatigue Properties of Ultrahigh-Strength Low Alloy TRIP-Aided Steels Reviewed

Tomohiko Hojo, Junya Kobayashi, Koh-ichi Sugimoto, Yoshito Takemoto, Akihiko Nagasaka, Motomichi Koyama, Eiji Akiyama

Tetsu-to-Hagane   107 ( 8 )   672 - 680   2021.8

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Publishing type：Research paper (scientific journal)   Publisher：Iron and Steel Institute of Japan  

DOI： 10.2355/tetsutohagane.tetsu-2021-015

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Effects of Matrix Structure and Nitrogen Content on Fatigue Properties of Ultrahigh-Strength Low Alloy TRIP-Aided Steels Reviewed

Tomohiko Hojo, Junya Kobayashi, Koh-ichi Sugimoto, Yoshito Takemoto, Akihiko Nagasaka, Motomichi Koyama, Eiji Akiyama

ISIJ International   61 ( 2 )   591 - 598   2021.2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Iron and Steel Institute of Japan  

DOI： 10.2355/isijinternational.ISIJINT-2020-392

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Decarburizing behavior and its effect on mechanical properties of ultrahigh strength steel sheets Reviewed

Kuwata Kentaro, Takemoto Yoshito, Okayasu Mitsuhiro, Bian Jian, Senuma Takehide

ISIJ International   61 ( 4 )   1300 - 1308   2021

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In this study, the decarburization behavior, and its effect on mechanical properties of 2 000 MPa class martensitic steel were investigated with the purpose of collecting the basic data to realize the further strengthening of structural members for automobiles. Concerning the decarburization behavior, the maximum of the decarburization rate of 2 000 MPa class martensitic steel with a basic chemical composition of 0.35%C-1.2%Mn was found around 750°C and the thickness of the decarburized zone grew proportional to the square root of time. The addition of Nb reduced the decarburization rate. Concerning the effect of decarburization on mechanical properties, the decarburization significantly improved bendability even though the thickness of the decarburized layer is relatively thin. An observation of the crack behavior revealed that the initiation and propagation of the crack were suppressed by the decarburization layer. The resistance to delayed fracture was improved by decarburization. This improvement is presumed to be based on a similar mechanism for the improvement of bendability.

DOI： 10.2355/isijinternational.ISIJINT-2020-416

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Strain effects on spinodal decomposition in TiO2–VO2films on TiO2(100) substrates Reviewed

Yuji Muraoka, Fumiya Yoshii, Takahiro Fukuda, Yuji Manabe, Mikiko Yasuno, Yoshito Takemoto, Kensei Terashima, Takanori Wakita, Takayoshi Yokoya

Thin Solid Films   698   137854 - 137854   2020.3

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.tsf.2020.137854

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Strange phase transformation of Ti-10Mo-7Al alloy Invited Reviewed

Titanium Japan   67 ( 2 )   112 - 115   2019.2

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Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

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Control of Heterogeneous Microstructure for Improving Delayed Fracture Resistance of Ultrahigh Strength Hot Stamping Steel Sheets Reviewed

Takehide Senuma, Yoshito Takemoto, Tomohiko Hojo

TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN   105 ( 2 )   51 - 59   2019.2

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：IRON STEEL INST JAPAN KEIDANREN KAIKAN  

Toward a high demand for ultrahigh strength automotive components for reducing body weight and increasing crashworthiness, hot stamped components have been employed worldwidely, and the further increase in strength of hot stamped components is being requested. A large obstacle of the strength increase is the concern about the occurrence of delayed fracture.In this study, we investigated the effects of microstructure on the resistance to delayed fracture of hot stamped steel sheets from a viewpoint of the control of heterogeneous microstructure, and the following results were obtained:(1) The grain refinement of martensite increases the resistance to delayed fracture.(2) Samples containing some amount of ferrite in the martensite matrix have a lower or higher resistance to delay fracture than samples with full martensitic microstructure, depending on the morphology of ferrite.(3) The presence of residual austenite of several % increases the resistance to delayed fracture remarkably but if it is strained and transformed to martensite, the resistance to delayed fracture drastically decreases.(4) Concerning 2000 MPa class hot stamping steel sheets, a higher carbon steel quenched and tempered at low temperature has higher resistance to delayed fracture than a quenched lower carbon steel with the same strength.In the paper, we discussed these results including their mechanisms in detail.

DOI： 10.2355/tetsutohagane.TETSU-2018-079

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Martensitic Transformation Induced in Ti-15V-7Al Alloy at Low and High Temperatures Reviewed

Y. Takemoto, M. Tsunekawa, Y. Manabe, S. Itano and Y. Muraoka

Materials Transactions   59 ( 10 )   1560 - 1566   2018.10

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2320/matertrans.M2018185

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Multilayer formation via spinodal decomposition in TiO2-VO2 epitaxial films on sapphire substrates Reviewed

Y. Matsuura, F. Yoshii, T. Otsuka, K. Kadowaki, M. Ijiri, Y. Takemoto, K. Terashima, T. Wakita, T. Yokoya and Y. Muraoka

Journal of the European Ceramic Society   38   5043 - 5050   2018.8

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Change of Electrical Resistivity with Martensite Transformation of Ti-42mass%Nb Alloy Reviewed

J. Japan Inst. Met. Mater.   82 ( 7 )   256 - 261   2018.7

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Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.2320/jinstmet.J2018013

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Martensitic Transformation Induced at Low and High Temperatures on Ti-15V-7Al Alloy Reviewed

J. Japan Inst. Met. Mater.   82 ( 8 )   307 - 313   2018

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Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.2320/jinstmet.J2018014

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Effect of aliovalent dopants on the kinetics of spinodal decomposition in rutile-type TiO2-VO2 Reviewed

Makoto Ogata,Kenji Kadowaki,Masataka Ijiri,Yoshito Takemoto*,Kensei Terashima*,Takanori Wakita*,Takayoshi Yokoya*,Yuji Muraoka*

Journal of the European Ceramic Society, International Journal of High Technology Ceramics   37 ( 9 )   3177 - 3183   2017.8

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jeurceramsoc.2017.03.039

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Stress-Strain Behavior of Ti-Nb Alloys under Compressions along Linear Strain Paths and Bilinear Plane Strain Path Reviewed

SHIMIZU Ichiro, TAKEMOTO Yoshito, ISHIKAWA Shinichi, KUMURA Tomohiro

Advanced Experimental Mechanics   2   99 - 104   2017.7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Society for Experimental Mechanics  

<p>Titanium alloys containing beta stabilizing elements exhibit several superior properties compared to other conventional metals. However, there are unknowns about the mechanical behavior of titanium alloys under biaxial compressive stress conditions. In this study, uniaxial compression and biaxial compressions along linear strain paths and bilinear strain path were performed on titanium-niobium alloys (Ti-Nb alloys) in order to investigate the influence of Nb contents on the compressive deformation behaviors. The results of compressions along linear strain paths revealed that the flow stress decreased while the ductility increased with the increase of the Nb content. It was found that the phenomenon was mainly due to changes of the microstructure and the primary plastic deformation mechanism. Those changes also induce anisotropic hardening. Based on those results, quantitative expression of the stress-strain relation with taking into account the Nb contents was discussed. The investigation on the effect of strain path change on the flow stress revealed the niobium dependency of the stress-strain response before and after the abrupt strain path change.</p><p></p>

DOI： 10.11395/aem.2.0_99

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Influence of Nb Content of Ti-xNb-7Al Alloys on beta -&gt;alpha '' Transformation with Tempering Reviewed

Masataka Ijiri, Yuki Tomita, Takafumi Ishikawa, Kenji Kadowaki, Yoshito Takemoto

JOURNAL OF THE JAPAN INSTITUTE OF METALS   81 ( 7 )   345 - 351   2017

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

The purpose of this study is to investigate the influence of Nb content of Ti-xNb-7Al alloys (x= 20-35 mass%, abbreviated as xNbA) on beta (bcc) -&gt; alpha ''(orthorhombic) transformation with tempering through microstructure, isothermal age-hardening, and shape change of a U-shaped specimen with heating. Full alpha ''-martensite structure was obtained on the quenched 20 NbA. With increasing of Nb content, residual beta-phase increased, and single beta-phase was obtained in the alloys of more than 25 NbA. From the result, the M-S temperature commonly decreases with increasing of Nb content. The hardness of 20 NbA and 23 NbA rapidly increased in a few seconds by isothermal aging at 450 degrees C, and the hardness of the alloys of more than 25 NbA abruptly increased after an incubation period for 30-60 s. No compositional distribution between alpha '' and matrix in the aged 23 NbA was found by STEM-EDS analysis, but the obvious distribution of Nb was detected in 35 NbA. U-shaped specimen of 20 NbA exhibited no shape change by heating. On the other hand, the specimen of 23 NbA composed of beta+alpha '' phases showed the shape recovery (SR) first due to work induced alpha ''-&gt;beta inverse transformation, then deformed toward the bending direction (SA: shape advance) due to beta -&gt;alpha '' transformation. The specimens of more than 28 NbA composed of single beta-phase exhibited only SA without SR. The starting temperature of SA (M-SA: beta -&gt;alpha '') with heating increases with increasing of Nb content. Merging M-S(upper) and M-SA(lower), it is proposed that the whole M-S of xNbA alloy forms a bow shape curve. It is suggested that the low Nb alloys inside the M-S curve transform immediately without atom diffusion by tempering at 450 degrees C, but the higher Nb alloys outside the curve need an incubation period to distribute Nb concentration with atom diffusion, and martensitic alpha '' transformation will abruptly occur in the local domains less than 25 NbA which is the inside of the curve.

DOI： 10.2320/jinstmet.J2017011

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Influence of Nb and Mn content on resistance to delayed fracture of ultrahigh strength hot stamped steel sheets Reviewed

Takuya Kishimoto, Yoshito Takemoto, Takehide Senuma

6th International Conference Hot Steel Metal Forming of High-Performance Steel, CHS2 2017- Proceedings   187 - 194   2017

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Association for Iron and Steel Technology, AISTECH  

One of the important objectives of hot stamping technology is an increase in tensile strength up to 2000 MPa. The largest obstacle to the realization of the strength increase to this height is a concern over the occurrence of delayed fracture. However, the principle idea for designing chemical compositions and operational conditions for increasing the resistance to delayed fracture has not been established yet. In this paper, the effect of Mn and Nb on the resistance to delayed fracture has been investigated to obtain the principle idea for designing chemical compositions for increasing the resistance to delayed fracture of ultrahigh strength hot stamping steel sheets. The following results were obtained. Nb addition increased the resistance to delayed fracture. A decrease in added Mn also increases the resistance to delayed fracture. Detailed investigations on the effect of Nb and Mn on the resistance to delayed fracture indicated that these alloys in solution, especially segregated in the grain boundary, affected the resistance to delayed fracture. A key requirement to improve the delayed fracture property is to control the segregation behavior of Nb and Mn.

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Stress-Strain Behavior of Ti-Nb Alloys under Compressions along Linear Strain Paths and Bilinear Plane Strain Path Reviewed

SHIMIZU Ichiro, TAKEMOTO Yoshito, ISHIKAWA Shinichi, KUMURA Tomohiro

Advanced Experimental Mechanics   2   1 - 6   2016.11

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：The Japanese Society for Experimental Mechanics  

<p>Titanium alloys containing beta stabilizing elements exhibit several superior properties compared to other conventional metals. However, there are unknowns about the mechanical behavior of titanium alloys under biaxial compressive stress conditions. In this study, uniaxial compression and biaxial compressions along linear strain paths and bilinear strain path were performed on titanium-niobium alloys (Ti-Nb alloys) in order to investigate the influence of Nb contents on the compressive deformation behaviors. The results of compressions along linear strain paths revealed that the flow stress decreased while the ductility increased with the increase of the Nb content. It was found that the phenomenon was mainly due to changes of the microstructure and the primary plastic deformation mechanism. Those changes also induce anisotropic hardening. Based on those results, quantitative expression of the stress-strain relation with taking into account the Nb contents was discussed. The investigation on the effect of strain path change on the flow stress revealed the niobium dependency of the stress-strain response before and after the abrupt strain path change.</p><p></p>

DOI： 10.11395/aem.2.0_99

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Effect of Nb in Ti-xNb-7Al Alloys on Microstructure and Tempering Behavior Reviewed

Masataka Ijiri, Yuki Tomita, Takafumi Ishikawa, Yousuke Taguchi and Yoshito Takemoto

The Ninth Pacific Rim International Conference on Advanced Materials and Processing (PRICM9)   648 - 650   2016.8

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Effect of Stress Loading on Elastic Behavior of Quenched Ti-Nb Alloys Reviewed

Yoshikazu Mantani and Yoshito Takemoto

The Ninth Pacific Rim International Conference on Advanced Materials and Processing (PRICM9)   644 - 647   2016.8

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Shape Change Behavior and Microstructure with Tempering of Ti-10Mo-7Al Alloy Reviewed

Yoshito Takemoto, Masataka Ijiri and Tatsuya Tanaka

The Ninth Pacific Rim International Conference on Advanced Materials and Processing (PRICM9)   651 - 653   2016.8

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Oil-in-water emulsion as fabrication platform for uniform plasmon-controlled two-dimensional metallic nanoparticle array Reviewed

Ryusuke Kagawa, Nobuyuki Takeyasu, Takashi Kaneta, Yoshito Takemoto

APPLIED PHYSICS EXPRESS   9 ( 7 )   075003   2016.7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Gold/silver nanoparticles were trapped at the oil/water interface of oil droplets dispersed in water. The metallic nanoparticles were self-assembled into a uniform two-dimensional large array structure through the aggregation and coalescence of the nanoparticle-covered oil droplets. The plasmon resonance of the array structure was tunable and a surface-enhanced Raman scattering measurement was performed with the silver nanoparticle array. The enhancement factor was similar to 10(5) and enhanced Raman signals were observed over the whole array (greater than or similar to cm(2)) with high reproducibility, which is an advantage of a self-assembly method using a liquid/liquid interface. (C) 2016 The Japan Society of Applied Physics

DOI： 10.7567/APEX.9.075003

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Phase Transformation Behavior of Ti-35Nb-7Al Alloy with Tempering Reviewed

Masataka Ijiri, Yuki Tomita, Takafumi Ishikawa, Yoshito Takemoto

JOURNAL OF THE JAPAN INSTITUTE OF METALS   80 ( 9 )   547 - 552   2016

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

Certain beta-Ti alloys, Ti-4Fe-7Al and Ti-10Mo-7Al, the compositions of which are characterized by a 7% aluminum addition to the beta lower. limit compositions, exhibit an interesting phenomenon upon tempering. For example, these alloys drastically harden upon tempering at 450 degrees C for several seconds, and the sample surface becomes severely uneven. When a strip specimen is bent plastically or elastically into a U-shape and heated to 450 degrees C, the shape spontaneously deforms towards the inside, which is different from the behavior of shape-memory alloys. In this study, Ti-35Nb-7Al alloy was selected as a candidate novel alloy, and the microstructure, the characteristics of age hardening and the shape evolution of a U-shaped specimen upon heating were investigated. The quenched alloy was a single beta-phase, and its hardness was considerably higher than that of binary Ti-35Nb alloy. The smooth surface of the quenched specimen became uneven at around 300 degrees C upon heating. Either case of U-shaped specimen, which was plastically or elastically bent, exhibited spontaneous bending towards the inside by heating up. It was found that, with tempering, Ti-35Nb-7Al also exhibits the novel phenomenon, similarly to Ti-4Fe-7Al and Ti-10Mo-7Al. Fine needle-alpha '' and omega-particles were formed in the beta matrix after isothermal aging at 450 degrees C for 3 min and gave rise to a remarkable hardening. STEM. EDS analysis revealed that the Nb content decreased in the alpha '' products formed by tempering. Consequently, the beta -&gt;alpha '' transformation upon tempering on this alloy is accompanied with atomic diffusion. Extra spots at &lt; 100 &gt;*, such as those of the B2 structure, were observed in the selected. area diffraction patterns of the TEM foils prepared by common electropolishing techniques. However, a TEM foil prepared with an FIB ( focused ion beam) did not exhibit the extra spots. These results suggested that the extra spots were caused by hydrogen absorption in the specimen during electropolishing.

DOI： 10.2320/jinstmet.JAW201601

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Microstructure of Ti-4Fe-7Al Alloy Quenched in a Salt Bath after Solution Treatment Reviewed

Masataka Ijiri, Akira Okumura, Takafumi Ishikawa, Kenji Kadowaki, Yoshito Takemoto

JOURNAL OF THE JAPAN INSTITUTE OF METALS   80 ( 11 )   691 - 696   2016

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

The Ti-4Fe-7Al alloy exhibits some interesting phenomena upon tempering. The noteworthy features are rapid hardening and shape change in a U-shaped specimen with heating, which are caused by the beta(bcc) -&gt; alpha '' (orthorhombic) transformation at elevated temperature. The transformation behavior on the TTT ( time-temperature-transformation) diagram estimated from the age hardening at various temperatures indicated a C-curve with a nose at 450 degrees C, which means that the transformation occurs through a thermal activation process. However, STEM-EDS analysis of alpha '' revealed that the transformation had occurred without atom diffusion. In this study, every solution treatment was carried out at 1050 degrees C for 30 min under a vacuum, then the specimen was quenched into a salt bath of 200-550 degrees C and held for a certain period prior to water quenching. These treated specimens were compared with the quenched and tempered specimens with respect to the microstructure and the hardening behavior. The hardness of the specimens held at 200-500 degrees C (30 s) increased with increasing holding temperature. The maximum hardness, 610Hv, which was almost the same as that of a tempered specimen, was obtained at around 450 degrees C. The microstructure of the specimen held at 450 degrees C (30 s) showed a common morphology composed of acicular martensite variants, except for the size. Because the several variants would cancel the transformation strain of each other, no severe unevenness of the surface was generated, unlike the tempered specimen. On the other hand, the hardness of the specimen held at 550 degrees C (30 s) decreased drastically owing to the phase separation to alpha + beta, and the TiFe precipitates were generated from beta upon the extension of the holding time.
By the TEM observation of the electropolished thin foil of the specimen held at 450 degrees C (30 s), unreasonable microstructure that was different from the XRD result was obtained. Just after the electropolishing, the SAD patterns showed that the alpha '' structure has a commensurate relation with the beta-lattice. However, alpha '' turned spontaneously into an incommensurate relation after one year. On the other hand, TEM observations of the foil prepared by FIB (focused ion beam) were consistent with the XRD result. It was suggested that the hydrogen absorption during electropolishing caused a structural transition of alpha '' martensite.

DOI： 10.2320/jinstmet.J2016032

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Change in structure and mechanical properties of Ti-10Mo-7Al by heat treatments Reviewed

M. Ijiri, Y.Takemoto

Proc. and Fabrication of Advanced Materials -XXIV   318 - 324   2015.12

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Phase Transformation Behavior of Ti-10Mo-7Al Alloy with Heat Treatment Reviewed

Masataka Ijiri, Yoshito Takemoto

JOURNAL OF THE JAPAN INSTITUTE OF METALS   79 ( 9 )   468 - 473   2015.9

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Language：Russian   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

A novel phenomenon recently observed in the tempering of Ti-4Fe-7Al alloy, has attracted considerable attention. This phenomenon is induced by the beta -&gt;alpha '' transformation during tempering, and its noteworthy features are rapid hardening and a shape change in a U-shaped specimen. It is of interest whether this phenomenon occurs in other alloy systems. In this study, Ti-10Mo-7Al alloy, which contains a quantity of molybdenum corresponding to the lower beta limit, was prepared and its microstructure, aging behavior, and shape change during tempering were investigated. An acicular alpha '' martensites were observed preferentially at the beta grain boundaries in the quenched specimen, but it became invisible at the optical microscope level upon tempering. However, TEM (transmission electron microscopy) observation of the tempered specimen revealed nano size martensites instead of micron-size martensites. The novel phenomenon observed in the tempering of Ti-4Fe-7Al, was also confirmed to occur in Ti-10Mo-7Al alloy. In the heating of a U-shaped specimen, shape recovery occured first, then a shape return into a U-shape followed, and a curvature progressed more with increasing of temperature. As a result, the phenomenon was clarified to be a universal one. The transformation mechanism through tempering is explained as follows: Though aluminum addition to beta-alloy raises the M-S chemically, on the other hand, it causes a remarkable solution strengthening, which increases shear stress required for martensite transformation, and decreases the apparent M-S. Consequently, the beta phase is maintained by a rapid cooling. However, temperature rise decreases the shear stress, and the apparent M-S increases to a chemically intrinsic one. If the M-S increases beyond the tempering temperature, martensite transformation occurs abruptly.

DOI： 10.2320/jinstmet.J2015027

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Change in Crystal Structure and Material Properties with Deformation of Quenched Martensite in Ti-Nb Alloys Reviewed

Yoshikazu Mantani, Yoshito Takemoto

JOURNAL OF THE JAPAN INSTITUTE OF METALS   79 ( 9 )   461 - 467   2015.9

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Language：Russian   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

The purpose of this study was to investigate and discuss the relationship between the crystal structure of martensites and the material properties, such as the Young's modulus and internal friction, in quenched Ti-Nb alloys with plasto-elastic deformation. In the alloys, minimal Young's modulus was indicated by the alpha' martensite of Ti15Nb, and maximal internal friction was indicated by the alpha '' martensite of Ti18Nb. After a weak plastic deformation of 5% rolling reduction, the Young's modulus of Ti-(15, 18, 20)Nb decreased, and the internal friction of Ti20Nb increased though that of Ti-(15, 18)Nb hardly changed. From the XRD profiles, the extreme values of the material properties were predicted to be associated with the unit volume and phases (hexagonal close-packed or orthorhombic) of the materials. It was also predicted to be associated with the change of phase from alpha' to alpha '' and from alpha '' to alpha' + alpha '' or alpha '' + alpha '' with different lattice parameters. Cyclic tensile test results after weak plastic deformation revealed characteristic changes in elastic incline, that is, an increase from similar to 40 GPa in Ti15Nb, and a decrease until similar to 40 GPa from the initial value followed by an increase in Ti18Nb and Ti20Nb. The consequent changing mechanism of material properties was suggested from the viewpoint of the changing behavior of the phase transformation and transition on martensites with plastic deformation or loaded elastic deformation.

DOI： 10.2320/jinstmet.JAW201506

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Alloy Composition Dependency of Plastic Deformation Behavior in Biaxial Compressions of Ti-Nb Alloys Reviewed

Ichiro Shimizu, Kazuki Hisada, Shinichi Ishikawa, Yoshito Takemoto, Naoya Tada

INTERNATIONAL CONFERENCE ON EXPERIMENTAL MECHANICS 2014   9302   2015

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Crystal structure of titanium alloy changes from alpha (hexagonal close-packed) to beta (body centered cubic) with increase of beta stabilizer content. This change of structure strongly influences on the plastic deformation behavior of titanium alloys, because it not only induces changes of slip systems but also activates martensitic transformation and deformation twinning. However, most of past studies on titanium alloys have been focused on the development of specific functionalities induced by alloy designing, and few research works have been reported on metal workability under multi-axial stress conditions, which is key factor to apply titanium alloys for engineering products. In this study, uniaxial and biaxial compression tests of titanium-niobium alloys with various niobium contents have been performed to clarify the influence of beta stabilizer content on the plastic behavior under compressive stress conditions. The titaniumniobium alloys were solution treated and then quenched from beta region to obtain metastable structures. The resultant stress-strain relations together with microscopic observations of texture revealed that the influence of niobium contents on the predominant plastic deformation mechanisms and thus on the hardening phenomena. The equi-plastic work contours obtained by uniaxial and biaxial compression tests also implied the crystal structure dependency of anisotropic hardening, which was evaluated quantitatively by means of Hill's anisotropic yield criterion. The results will provide information on the versatile constitutive relations of titanium alloys containing beta stabilizer elements, that is important to prove the performance of products manufactured by compressive metal working processes such as forging and extrusion.

DOI： 10.1117/12.2077324

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Influence of Microstructures on Hydrogen Embrittlement Susceptibility of Hot Stamped Ultrahigh Strength Components Reviewed

Masahiro Matsumoto, Yoshito Takemoto, Takehide Senuma

HOT SHEET METAL FORMING OF HIGH-PERFORMANCE STEEL CHS2 (5TH INTERNATIONAL CONFERENCE)   ( 5 )   55 - 63   2015

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：VERLAG WISSENSCHAFTLICHE SCRIPTEN  

One of large hindrances against the increase in the strength of hot stamped components is an increasing risk of the occurrence of delayed fracture. In this study, the influence of microstructures on the hydrogen embrittlement susceptibility of hot stamped ultra-high strength components has been investigated. The following results were obtained.
The grain refinement of martensite reduces the hydrogen embrittlement susceptibility. The bake hardening (BH) treatment through which the lattice stress is released and fine ferrous carbides are precipitated suppresses the delayed fracture significantly. A presence of small amount of ferrite in the martensite microstructure hardly decreases the resistance to delayed fracture. A proper presence of nano-scale precipitates delays the occurrence of the delayed fracture. The precipitation control which creates the proper precipitates trapping hydrogen effectively and suppressing the delayed fracture will be discussed in the paper.
The obtained results indicated that hot stamped components with a tensile strength of more than 2000 MPa without great risk against the delayed fracture can be produced by a sophisticated microstructural control.

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ホットスタンピングの成形性ならびに生産性向上技術 Reviewed

瀬沼武秀,竹元嘉利

鉄と鋼   100 ( 12 )   1481 - 1489   2014.12

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Influence of Predeformation on Tempering Structure of Ti-5Al-2Fe-3 Mo Alloy Reviewed

Yoshito Takemoto, Keita Wada, Kenta Asakura, Takehide Senuma, Tomonori Kunieda, Hideki Fujii

JOURNAL OF THE JAPAN INSTITUTE OF METALS   78 ( 12 )   434 - 440   2014.12

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A near-beta-type Ti-5Al-2Fe-3Mo alloy (Super-TIX (R) 523AFM) was developed as a low-cost and high-strength material for automotive components such as intake valves. Its mechanical properties, such as strength, elongation and Young's modulus, are adjustable via the solution treatment temperature. Furthermore, a unique phenomenon different from the shape memory effect that appears after tempering has recently been discovered in the alloy. In this study, the influence of predeformation on the microstructural evolution attributed to the tempering of the alloy quenched from 900 degrees C (alpha + beta) was investigated to clarify the cause of the unique phenomenon. Although the phase constitution of the quenched specimen was alpha + beta, the effective Mo equivalency (6.5Mo(effeq)) of the phase was lower than the minimum beta composition (10Mo(effeq)) in common beta alloys. Work. induced alpha" martensite plates consisting of single alpha" variant including nanosize beta domains were formed in the beta-phase by cold-rolling. Upon heating the rolled specimen to around 250 degrees C, the plates vanished owing to the alpha"-&gt;beta inverse transformation and the hardness decreased. However, when the rolled specimen was heated to 450 degrees C, the hardness markedly increased as a result of the beta -&gt;alpha" transformation, and the plates were formed again. The plates consist of a single alpha" variant, but the alpha" lattice is not extensively continuous and is divided into nanosize domains by boundaries containing many faults. It is considered that the evolution of single-alpha"-variant plates generates a large distortion due to the transformation strain and leads to the unique shape change. Such plates were not formed in undeformed specimen by aging at 450 degrees C, and the beta-phase was transformed into a nanosize domain structure composed of multiple alpha" variants. Consequently, these fine structure in the undeformed specimen led to its higher hardness than that of the rolled specimen.

DOI： 10.2320/jinstmet.J2014035

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V単独，V-Nb複合添加超高強度ホットスタンピング部材の組織と機械的性質 Reviewed

立山 祥大, 石尾 遼平, 林 公平, 須江 龍裕, 竹元 嘉利, 瀬沼 武秀

鉄と鋼   100 ( 9 )   1114 - 1122   2014.9

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Formability and Productivity Improving Technology of Hot Stamping Reviewed

Takehide Senuma, Yoshito Takemoto

TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN   100 ( 12 )   1481 - 1489   2014

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：IRON STEEL INST JAPAN KEIDANREN KAIKAN  

As a method for producing ultrahigh strength automotive steel components with high gauge accuracy the hot stamping technology draws attention and is practiced widely today. For supporting and developing this technology, numerous researches have been actively carried out all over the world. It is a good timing to review this technology on this special issue because further rapid development is to be expected in the next decade. The hot stamping technology consists of a variety of techniques. In this review, the authors focus two items suitable to this special issue, the first one is the formability of hot stamping and the second is the technology for improving its productivity.
The review shows the importance of the temperature control at stamping parts to achieve excellent formability. Through the review on the technology for improving the productivity of hot stamping, the authors propose highly productive hot stamping processes consisting of rapid heating, short time stamping and rapid cooling.

DOI： 10.2355/tetsutohagane.100.1481

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Microstructures and Mechanical Properties of V and/or Nb Bearing Ultrahigh Strength Hot Stamped Steel Components Reviewed

Shota Tateyama, Ryohei Ishio, Kouhei Hayashi, Tatsuhiro Sue, Yoshito Takemoto, Takehide Senuma

TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN   100 ( 9 )   1114 - 1122   2014

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：IRON STEEL INST JAPAN KEIDANREN KAIKAN  

As a method for producing ultrahigh strength automotive steel components with high gauge accuracy, the hot stamping technology draws attention and the amount of hot stamped automotive components has exponentially increased in the last decade. The concerns about the potential danger of embrittlement and delayed fracture, however, limit the strength of conventional hot stamped components to 1500 MPa. If these concerns are eliminated, automotive steel components with higher strength which is demanded by the automotive industry can be further commercialized.
In this study, microstructures and mechanical properties of V and/or Nb bearing ultrahigh strength hot stamped steel components have been investigated. The V addition improves the resistance to delayed fracture by forming VC whose interface with matrix is supposed to act as preferential hydrogen trap site. The Nb addition refines the microstructure, which improves both the toughness and the resistance to delayed fracture. Proper hot stamping conditions for these steels has been discussed to create an ultrafine martensite microstructure and finely dispersed precipitates. The results indicate that 1900 MPa class steel components with good toughness and high resistance to delayed fracture can be produced.

DOI： 10.2355/tetsutohagane.100.1114

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V,Cuの単独ならびに複合添加中炭素鋼の析出硬化挙動 Reviewed

鉄と鋼   99 ( 11 )   669 - 675   2013.11

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Influence of Various Factors on the Refinement of Martensitic Microstructures of Hot Stamped Steel Components Reviewed

Ono Takafumi, Hosomi Tsukasa, Takemoto Yoshito, Senuma Takehide

Tetsu-to-Hagane   99 ( 7 )   475 - 483   2013.7

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Iron and Steel Institute of Japan  

The toughness and the resistance to delayed fracture are deteriorated with increasing strength of martenstic steels. It has been reported that these properties could be improved by grain refinement of martensite.<br>In this study, the influence of both hot stamping conditions such as heating rate, heating temperature, cooling rate, and material conditions such as hot band microstructure, cold rolling reduction, addition of micro-alloys on the grain refinement of hot stamped ultra-high strength martenstic steel components are investigated. The investigation revealed that low temperature and short time heating, high heating and cooling rates, the decrease in the coiling temperature of hot bands, the increase in cold rolling reduction and addition of micro-alloys are preferable for grain refinement of martensite. The mechanism of the grain refinement was discussed from the viewpoints of the increase in the nucleation rate of austenite during the α→γ transformation and the suppression of the austenite grain growth.

DOI： 10.2355/tetsutohagane.99.475

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Hydrogen Embrittlement Properties of Ultra High-Strength Low Alloy TRIP-Aided Steels with Hot Forging Process Reviewed

Proc. of the 2nd. Int. Sympo. on Automobile Steel   169 - 172   2013.5

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ホットスタンピング部材の生産性向上ならびに高機能化のための組織制御 Reviewed

塑性と加工   54   137 - 142   2013.2

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Development of 2000MPa Class Hot Stamped Steel Components with Good Toughness and High Resistance against Delayed Fracture Reviewed

Akitaka Tokizawa, Kousuke Yamamoto, Yoshito Takemoto, Takehide Senuma

HOT SHEET METAL FORMING OF HIGH-PERFORMANCE STEEL CHS2 (4TH INTERNATIONAL CONFERENCE)   ( 4 )   473 - 479   2013

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：VERLAG WISSENSCHAFTLICHE SCRIPTEN  

Although higher strength of hot stamped automotive components is demanded, the strength higher than 2000 MPa is not realized because of the deterioration of toughness and resistance against delayed fracture.
In this study, we investigated a proper microstructural control to achieve a good strength-toughness balance with high resistance against delayed fracture. As a result, we have determined the condition for producing 2000 MPa class hot stamped components with the toughness and anti-delayed fracture property which are nearly equal to or better than those of conventional 1500 MPa class components. The microstructure of the hot stamped components consists of ultrafine grained martensite matrix with finely dispersed ferrous carbides and alloy precipitates. The grain refinement of martensite implies to improve toughness and the existence of fine ferrous carbides and alloy precipitates indicate to increase the sites trapping hydrogen and to raise the resistance against delayed fracture.

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Precipitation Hardening Behavior of V and/or Cu Bearing Middle Carbon Steels Reviewed

Yuuki Murase, Naoyuki Iwasa, Yoshito Takemoto, Takehide Senuma

TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN   99 ( 11 )   669 - 675   2013

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IRON STEEL INST JAPAN KEIDANREN KAIKAN  

In this study, the precipitation hardening behavior of middle carbon steels with single and multiple additions of 0.3mass%V and 2mass%Cu has been investigated. The precipitation treatment was carried out isothermally at 550 degrees C, 600 degrees C and 650 degrees C.
In the 0.3mass%V bearing steel, precipitation hardening was observed at 600 degrees C and 650 degrees C while no significant increase in hardness was observed at 550 C. When 2mass% Cu was added to the 0.3mass%V bearing steel, the hardness attributed to the precipitation hardening of Cu was added to that attributed to the precipitation hardening of VC in the cases of 600 degrees C and 650 degrees C. In the case of 550 degrees C, the V addition into the Cu bearing steel markedly increased the hardness although the precipitation hardening of VC was hardly observed in the 0.3mass%V bearing steel. In the paper, the different precipitation hardening behavior of the three steels is discussed in detail in consideration of the observed precipitation behavior.

DOI： 10.2355/tetsutohagane.99.669

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Peculiar Transformation Behavior and Microstructure Evolution with Tempering of Ti-4Fe-7Al Alloy Reviewed

Yoshito Takemoto, Kazuya Fujii, Shou Nakastuka, Takehide Senuma

JOURNAL OF THE JAPAN INSTITUTE OF METALS   77 ( 9 )   368 - 374   2013

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

The transformation behavior and microstructural changes of Ti-4Fe-7Al alloy during tempering were investigated by performing a hardness test and using X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. Within a brief time of 30 s during tempering at 450 degrees C, the hardness rapidly increased to a maximum value of 600 Hv. The transformation behavior estimated from the increase in hardness indicated "a lower half of C-curve" in the TTT diagram, which suggests that the transformation occurs through certain thermal activation processes. However, it is difficult to assume that the transformation is controlled by the diffusion of substitutional atoms, since the mean diffusion distance of Fe atoms during tempering at 300 degrees C for 1 x 10(3) s, which also maximized the hardness, is much less than the distance of the nearest neighbors in the beta structure. The structure of the alpha '' phase formed by tempering depends on both the temperature and holding time; a high temperature and a long time bring the alpha '' phase close to an hcp structure. As determined by XRD measurement, the sample tempered at 150 degrees C for 60 min was composed of the beta phase. However, the omega and alpha '' phases were also detected in selected area diffraction (SAD) patterns. The sample tempered at 450 degrees C for 60 min consisted of a single alpha '' phase and exhibited a tweed structure in the TEM observation. Although the tweed structure seemed to contain only one alpha ''-variant in the SAD patterns, HR-TEM observation revealed that it was composed of multiple nanoscale variants. It was considered that the marked grain refinement due to the nanoscale variants led to the extreme hardening of the sample and the significant broadening of XRD peaks. When the tempering temperature was increased to 600 degrees C, the a phase and finely dispersed TiFe precipitates were formed after 60 min by the diffusion of atoms, which resulted in the softening of the sample and the sharpening of the XRD peaks.

DOI： 10.2320/jinstmet.J2013027

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Microstructural Control in Hot Stamping Processes for Producing Ultra-high Strength Automotive Steel Components Reviewed

Takehide Senuma, Yoshito Takemoto, Kenichi Shimizu, Tomohiko Hojo

TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN   98 ( 11 )   751 - 758   2012.11

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Unprecedented Phenomena with Tempering of Ti-4Fe-7Al Alloy Reviewed

Yoshito Takemoto, Masahiro Ochi, Takehide Senuma, Jun Takada, Ichiro Shimizu, Kazuhiro Matsugi

JOURNAL OF THE JAPAN INSTITUTE OF METALS   76 ( 7 )   449 - 455   2012.7

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Unprecedented phenomena were discovered by tempering the Ti-4Fe-7Al alloy quenched from the beta (bcc) field. The alloy became very hard when it was tempered at 450 degrees C for several minutes, and severely rugged surface was generated. The inverse shape recovery phenomenon was also discovered when a quenched specimen that had been bent at room temperature was heated. The tempered microstructure showed almost beta grains and some of the usual martensitic acicular structure areas. However, electron back scattering pattern (EBSP) measurements showed that the beta-like grain was not the bcc structure but was the hcp or orthorhombic structure. X-ray diffraction (XRD) measurements clarified that an orthorhombic alpha '' structure (a = 0.299(5) nm, b = 0.491(3) nm, c=0.465(9) nm) was formed from the beta phase by tempering. Moreover, this a '' structure was confirmed to be a type of martensitic transformation because no concentration distribution was detected in scanning transmission electron microscopy-energy dispersive spectroscopy (STEM-EDS) analysis of the microstructure. It was suggested that the essential M-s point of the alloy should be higher than room temperature; however, the martensite transformation could not operate by fast quenching.
The newly-discovered alpha '' martensite is formed without atomic diffusion by heating. When the beta grain transforms into the single alpha ''-variant, a very huge lattice strain is generated, resulting in the severely rugged surface or the inverse shape recovery phenomenon.

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Tensile Properties and Work-hardening Behavior of Fe-3%Al Single Crystal Reviewed

Yoshito Takemoto, Takehide Senuma

TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN   98 ( 6 )   216 - 222   2012.6

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Synopsis: The tensile deformation behavior of single and poly-crystal Fe-3%Al alloys was investigated at room temperature. The work hardening rate (WEIR) of the polycrystalline alloy monotonously decreased with increasing strain and increased with decreasing grain size. The WHR of the single crystal alloy was remarkably lower than that of the polycrystalline alloy, and the single crystal alloy exhibited a peculiar behavior that could be classified into four different types depending on the tensile axes. When the tensile axes were on the line connecting &lt; 102 &gt; and &lt; 101 &gt; in the stereo triangle, the characteristics of deformation of the single crystal alloy were steady and its WHR showed a monotonous decrease similar to that observed in the case of the polycrystalline alloy. For most of the tensile orientations, including &lt; 001 &gt;, the WHR curve changed from concave to convex with a strain increase. The WHR for the &lt; 101 &gt; orientation also showed the maximum and minimum values, i.e., it dropped immediately after reaching the maxima. This behavior was considered ascribable to the transition of the dislocation structure. The deformation for the &lt; 111 &gt; orientation was characterized by the highest yield stress and work softening, which were caused by some intense slip bands with discontinuous stress drops. Lattice rotation with tensile deformation in single crystal alloys was also examined by an electron backscatter diffraction (EBSD) measurement. For determining the rotation direction, the stereo triangle was divided into two areas by a great circle connecting &lt; 113 &gt; and &lt; 102 &gt;.

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Influence of Al Addition on Microstructures and Mechanical Properties of Ti-Fe Alloys Reviewed

Yoshito Takemoto, Masahiro Ochi, Takehide Senuma, Jun Takada, Ichiro Shimizu, Kazuhiro Matsugi

JOURNAL OF THE JAPAN INSTITUTE OF METALS   76 ( 5 )   332 - 337   2012.5

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The influence of Al content on the evolution of microstructures and mechanical properties of Ti-xFe-yAl alloys quenched from a beta field was investigated via hardness measurements, tensile tests, scanning electron microscopy (SEM) equipped with electron back scattering pattern (EBSP) analyzer, and conventional transmission electron microscopy (TEM). The hardness of Ti-(3-6)Fe-yAl decreased remarkably on addition of 1% Al. In comparison to binary alloys, the maximum hardness decrease was achieved in Ti-4Fe-1Al. The hardness of Ti-4Fe-yAl decreased with increasing Al content up to around 5%, reaching a minimum, then gradually increased. Though all of the Ti-3Fe-yAl alloys showed the martensite structure, Ti-4Fe-yAl showed a structural change of beta + omega -&gt; beta + omega + martensite -&gt; beta + omega with increasing Al content. Consequently, Ti-4Fe-7Al had the lowest density in the beta-type alloys equivalent to that of Ti-6Al-4V. The ratio of reciprocal distance d(0002 omega)*/d(222 beta)* on selected-area diffraction (SAD) pattern, which is often used as an indicator of {332}&lt; 113 &gt; twin formation, was nearly constant up to 5% Al of Ti-4Fe-yAl, but decreased over 6% Al. The tensile tests of both Ti-4Fe-5Al and Ti-4Fe-7Al showed ductility. The deformation behavior of Ti-4Fe-5Al producing strain-induced martensite resembled that of Ti-8Mo. On the other hand, Ti-4Fe-7Al was deformed by a coarse slip of {112}&lt; 111 &gt; in the same manner as Ti-20Mo, and the SAD pattern analysis revealed that the diffuse reflection of the omega phase in the non-deformed area turned into the spots at the deformation band. It was suggested that Al behaves as a beta stabilizer element when added to the lowest beta alloy and is available for weight saving, while maintaining the beta structure.

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MODEL for PREDICTING RECRYSTALLIZATION BEHAVIOR OF COLD ROLLED EXTRALOW CARBON STEEL SHEETS Reviewed

Takehide Senuma, Yoshito Takemoto

THERMEC 2011, PTS 1-4   706-709   2302 - 2307   2012

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TRANS TECH PUBLICATIONS LTD  

Microstructual observations indicate that the recrystallization of cold rolled extralow carbon steel sheets occurs due to the abnormal growth of selected subgrains in recovered subgrain microstructures.
The authors measured the orientations of a recovered microstructure of a cold rolled extralow carbon steel sheet by SEM-EBSP and classified the deformed grains into several types due to the orientation and its scattering degree.
In this study, a model for predicting the recrystallization behavior of cold rolled extralow carbon steels has been developed by applying the model of Humphreys modified to the grain of each type. A good agreement between the experimental and calculated results using the model developed was obtained.

DOI： 10.4028/www.scientific.net/MSF.706-709.2302

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Microstructural Evolution of Carbon Steels in Hot Stamping Processes Reviewed

Kenta Hidaka, Yoshito Takemoto, Takehide Senuma

ISIJ INTERNATIONAL   52 ( 4 )   688 - 696   2012

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IRON STEEL INST JAPAN KEIDANREN KAIKAN  

Hot stamping is a very promising method for producing ultrahigh-strength automotive components. The heating and cooling conditions in the conventional hot stamping process are quite limited. To improve the productivity of the process and/or the mechanical properties of the product, optimizing the heating and cooling conditions is an important and urgent research subject.
In this study, the influence of the heating rate, heating temperature, and cooling conditions on the microstructure and mechanical properties of 0.22%C-2.5%Mn steel was investigated. Samples were heated at two different heating rates (10 degrees C/s and 200 degrees C/s) to various temperatures and then either cooled in air or quenched using water sprays. The sample heated at 200 degrees C/s to 800 degrees C and then immediately quenched in water exhibited a very fine martensite microstructure haying a grain size with an average diameter of 4 mu m and a hardness value around 550 Hy. The sample heated above Ac3 and subsequently cooled in air exhibited a full martensite microstructure and a hardness of 450 Hy. A model that predicted the precipitation of cementite during cooling was developed to clarify the cause of the difference in hardness of the martensite in the samples that were quenched in water and cooled in air. The calculations showed that the hardness of samples cooled in air was lower mainly because of the decrease in the solid solution hardening of C owing to the precipitation of cementite below the Ms temperature. Drawing on the results obtained, hot stamping technology is discussed and favorable operational conditions proposed.

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Influence of Ti and Nb on the Strength-Ductility-Hole Expansion Ratio Balance of Hot-rolled Low-carbon High-strength Steel Sheets Reviewed

Kyohei Kamibayashi, Yutaka Tanabe, Yoshito Takemoto, Ichirou Shimizu, Takehide Senuma

ISIJ INTERNATIONAL   52 ( 1 )   151 - 157   2012

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IRON STEEL INST JAPAN KEIDANREN KAIKAN  

To satisfy the demand for high-strength steel sheets with excellent strength-ductility-hole expansion ratio balance, high-strength steels consisting of a ferrite or bainitic ferrite matrix strengthened by a large amount of finely dispersed precipitates have been developed.
In this study, the influence of the precipitation-forming elements Ti and Nb on the strength-ductility-hole expansion ratio balance of these steels has been investigated. The strength-ductility-hole expansion ratio balance of steel with Ti added was superior to that with Nb added. The reason for the superiority of steel with added Ti was discussed from various viewpoints such as microstructure, texture, the condition of the pierced surface, sulphide formation, the nucleation and propagation behaviour of cracks during hole expansion, etc. We concluded that the inferior strength-ductility-hole expansion ratio balance of the steel with added Nb was mainly caused by the formation of large textural colonies and a detrimental influence of MnS. From these inferences, we proposed a combined addition of Ti and Nb, and succeeded in improving the strength-ductility-hole expansion ratio balance of the advanced high-strength steel.

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Effect of Rapid Heating on Evolution of Microstructures and Coating Layers in Hot Stamping Processes Reviewed

Proc. of the 3nd Int.Conf. Hot Sheet Metal Forming of High-Performance Steel   465 - 472   2011.6

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極低炭素冷延鋼板の再結晶モデル Reviewed

鉄と鋼   97 ( 4 )   238 - 244   2011.4

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Model for Predicting Recrystallization Behavior of Colled Rolled Extralow Carbon Steel Sheets Reviewed

Norihisa Nishitani, Takafumi Hiramoto, Yoshito Takemoto, Takehide Senuma

TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN   97 ( 4 )   238 - 244   2011.4

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Microstructual observations indicate that the recrystallization of cold rolled extralow carbon steel sheets occurs due to the abnormal growth of selected subgrains in recovered subgrain microstructures. Based on this recrystallization mechanism, a new model for predicting the recrystallization behavior of a material with idealized microstructure was proposed by Humphreys. The model cannot, however, predict the recrystallization behavior of cold rolled steel sheets in the practice because of the complexities of their microstructure.
In this study, a model for predicting the recrystallization behavior of cold rolled extralow carbon steels has been developed based on the model by Humphreys. The feature of the present model is that the pinning and solute drag effects on the recrystallization behavior can be evaluated quantitatively.
Using the model, the influence of Ti addition on the recrystallization in extralow carbon steel sheets was discussed. The result indicates that the retardation of the recrystallization due to the addition of Ti is attributed mainly to the retardation of the subgrain formation in the recovery process, and the effect of the pinning of precipitates and the dragging of solute Ti atoms on the progress of recystallization are relatively small.

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Influence of Alloying Elements on Precipitation Behavior of VCN in Middle Carbon Steels Reviewed

Takehide Senuma, Yoshito Takemoto

SOLID-SOLID PHASE TRANSFORMATIONS IN INORGANIC MATERIALS, PTS 1-2   172-174   408 - +   2011

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For lightening the hot forged automotive components such as connecting rods, crank shafts etc. the increase in their yield strength is an important technical issue. Recent developments indicate that it is a promising way to increase the yield strength of the components using the ferrite-pearlite microstructure strengthened by precipitation hardening of VC.
In this study, the influence of alloying elements, cooling rate and aging temperature on the precipitation hardening behavior of V containing middle carbon steels was investigated. The precipitation hardening is very sensitive to cooling rate and aging temperature. The addition of Si reduced the sensitivity of the cooling rate. The deformation in the austenite region slightly decreases the precipitation hardening. From a detailed analysis, it was found out that the precipitation hardening is strongly influenced by the gamma -&gt;alpha transformation behavior, which indicates that the interphase precipitation plays a significant role for the precipitation hardening.

DOI： 10.4028/www.scientific.net/SSP.172-174.408

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高効率多段ホットスタンピング技術 Reviewed

瀬沼武秀,馬込英明,葉賀一太,藤岡尚浩,竹元嘉利,清水憲一

塑性と加工   51 ( 7 )   54 - 58   2010.7

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Present Status and Future Perspective of Hot Stamping Technology : Key Technology for Lightening Automotive Bodies Reviewed

SENUMA Takehide, TAKEMOTO Yoshito

Journal of the JSTP   51 ( 592 )   410 - 415   2010.5

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DOI： 10.9773/sosei.51.410

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組織と特性予測の計算工学共通試料試験結果 Reviewed

計算工学による組織と特性予測技術の最前線 日本鉄鋼協会編   249 - 250   2010.5

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Influence of Thermal History on Microstructure and Mechanical Properties of Steels for Hot Stamping Reviewed

Takehide Senuma, Yoshito Takemoto

PRICM 7, PTS 1-3   654-656   330 - 333   2010

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Hot stamping is an attractive method to produce extra high strength automotive components. in the conventional hot stamping, the furnace heating is employed and the heating rate is quite low. To improve the productivity of the hot stamping technology, the reduction of time for the heating process is required. In this study, the influence of the heating rate in a range up to 200 degrees C/s, heating temperatures between 650 degrees C and 950 degrees C and cooling condition on microstructure and mechanical properties of 0.22% C -3%Mn steel has been investigated. The steel is a promising material for the highly productive new hot stamping technology because this steel transformed into martensite from austenite even at cooling in free air. The specimens heat-treated at a high heating rate and for short holding time at the heating temperature just above Ac3 show significantly fine martensite microstructure and a good strength-toughness balance. In this paper, the alpha --&gt; gamma transformation behavior and the gamma --&gt; alpha transformation behavior after inter-critical annealing are discussed to explain the evolution of the microstructures and mechanical properties.

DOI： 10.4028/www.scientific.net/MSF.654-656.330

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S0304-1-3 Evaluation of Crystal Orientation of Ti-Mo Alloys Using Micro Indentation Test

KIMURA Noriaki, SHIMIZU Ichiro, TADA Naoya, TAKEMOTO Yoshito

The proceedings of the JSME annual meeting   2010   265 - 266   2010

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In recent years, β-type Ti alloys have been attracting much attention for industrial applications, not only by its high specific strength and superior formability but also by special features such as low elastic modulus and extraordinary plastic deformation behavior. However, the studies on β-Ti alloys are still less than those on other types of Ti alloys. Hence, the evaluation processes of various properties of β-Ti alloys have still not been established nevertheless of their importance for industrial applications. The aim of the present study is to evaluate the crystal orientation of grains of β-Ti alloys by means of micro indentation technique. Ti-14Mo and Ti-20Mo alloys, whose primary deformation mechanisms are mechanical twin and coarse slip, respectively, were employed as typical β-Ti alloys. The detailed investigations were performed on the relationship between the crystal orientation and the indentation behavior. The results revealed that the lines which appeared around the indentation of Ti-14Mo almost corresponded to twin boundaries, while those of Ti-20Mo were slip lines. The distortion of indentation shapes also appeared on both Ti-Mo alloys. Based on these results, the procedure of crystal orientation evaluation by micro indentation test was discussed.

DOI： 10.1299/jsmemecjo.2010.1.0_265

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Ti-MoおよびTi-6Mo-X-Y合金の微細組織と機械的性質 Reviewed

竹元嘉利, 三宅章義, 瀬沼武秀

日本金属学会誌   73 ( 9 )   752 - 757   2009

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DOI： 10.2320/jinstmet.73.752

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Influence of Press Forming Conditions on the Shape Fixability of Hot Stamped Hat-type Parts Reviewed

Proc. of the 3rd Int. Conf. on Steels in Cars and Tracks   230 - 235   2008.6

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Elasto-plastic behavior and its composition dependency of β-type Ti-Mo alloys Reviewed

Proceedings of JSEM   ( 8 )   274 - 276   2008.6

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ホットスタンピング部品の形状凍結性に及ぼす成形条件の影響 Reviewed

瀬沼 武秀, 馬込 英明, 田邉 章宏, *竹元 嘉利

塑性と加工   49 ( 567 )   321 - 325   2008.4

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Model for Predicting the Microstructural Evolution of Extralow Carbon Steels Reviewed

Takehide Senuma, Yoshito Takemoto

ISIJ INTERNATIONAL   48 ( 11 )   1635 - 1639   2008

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The microstructural evolution of extralow carbon steels in hot working processes has been studied. Considering the experimental results of the microstructural evolution of austenite and the transformation behavior, a metallurgical model for predicting the microstructural evolution of extralow carbon steels in hot working processes was developed. The model was applied to hot rolling processes to evaluate the quantitative effect of various operation conditions on the grain refinement of ferrite and the calculated results were found to correlate relatively well to experimental ones.

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Grain refinement of extralow-carbon steels in hot strip rolling

Takehide Senuma, Yoshito Takemoto

3rd International Conference on Thermomechanical Processing of Steels, TMP 2008   2008

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The effect of various operational parameters such as the finishing temperature, the final reduction, the cooling rate, the onset time for cooling after the final rolling in a hot strip rolling process on the grain refinement of hot rolled extralow carbon steel bands has been investigated. To analyze the experimental results, a metallurgical model for predicting the microstructural evolution of extralow carbon steels in hot working processes was developed. The calculated results were found to correlate relatively well to experimental ones and indicate that the effect of various operation conditions on grain refinement can be explained by considering the evolution of the dislocation density in austenite and the transformation temperature.

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Analysis of Fine Stress Fields in Metal Matrix Composites Using HOLZ Patterns Reviewed

M. Shibata, Y. Takemoto and I. Shimizu

Materials Science Forum   539-543   848 - 853   2007.7

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The effect of deformation mechanism on plastic behavior of β-type Ti-Mo alloys Reviewed

Ichiro Shimizu and Yoshito Takemoto

Ti-2007 Science and Technology   1   543 - 546   2007.6

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Anelastic behavior of Ti-8mass%Mo alloy by pre-deformation Reviewed

Yoshito Takemoto, Akira Sakakibara and Takehide Senuma

Ti-2007 Science and Technology   1   539 - 542   2007.6

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Recrystallization behavior and texture formation of rapidly annealed cold-rolled extralow carbon steel sheets Reviewed

Takehide Senuma, Kaoru Kawasaki, Yoshito Takemoto

MATERIALS TRANSACTIONS   47 ( 7 )   1769 - 1775   2006.7

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The influence of a heating rate up to 1000 degrees C/s on recrystallization behavior and texture formation of an extralow carbon steel sheet was investigated. To discuss the experimental results of this investigation, a mathematical model for predicting recrystallization behavior was developed. An analysis using the model shows that the heating rate influences the apparent thermal activation energy of recrystallization. At a higher heating rate, C dissolved from cementite and AlN precipitated during heating decreases and as a consequence the apparent thermal activation energy is lower. This can also be a valid explanation for the fact that recrystallization of a steel sheet coiled at low temperature is retarded. The main orientations of the recrystallization texture are weakened if the heating rate is increased. This tendency has already been observed at the initial stage of recrystallization. If the specimen is heated slowly up to the initial stage of recrystallization, the decrease in the intensity of the main orientations is reduced even though the heating rate subsequently increases. This result indicates that, concerning formation of the recrystallization texture, the heating rate mainly influences the nucleation process.

DOI： 10.2320/matertrans.47.1769

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Change of elastic behavior in binary beta-type Ti alloys with deformation Reviewed

Y Takemoto, L Shimizu, A Sakakibara, T Senuma

JOURNAL OF THE JAPAN INSTITUTE OF METALS   70 ( 2 )   110 - 113   2006.2

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The aim of this study is to systematically investigate the elastic behavior with deformation of the binary titanium alloys of TiMo, Ti-Nb and Ti-V. The stress-strain curve using cyclic load-unloading tensile test of alloys composed of alpha '' martensite, e.g. 20Nb and 8Mo, showed the peculiar pseudo-elastic behavior. A little higher content of beta-stabilizer alloys of 38Nb, 10-14Mo and 15-20V, which were composed of 6 and commensurate omega phases by quench, indicated the liner elasticity until the yield but changed to the extreme pseudo-elasticity after {332}&lt; 113 &gt; twin formation. Dynamic observation made clear certain {332}&lt; 113 &gt; twin initially formed on tensile loading disappeared during unloading process. Medium content of beta-stabilizer alloys of 42Nb and 16Mo exhibited a concave downward elastic curve and were deformed by mixture mode of slip and {332}&lt; 113 &gt; twin. On the higher content alloys it was found that the stress level on which Young's modulus begins a rise increases with the increase of alloy content. These elastic features were summarized as change of apparent Young's modulus with increase of strain.

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2元系β型チタン合金の変形に伴う弾性挙動変化 Reviewed

竹元嘉利, 清水一郎, 榊原精, 瀬沼武秀

日本金属学会誌   70 ( 2 )   110 - 113   2006

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DOI： 10.2320/jinstmet.70.110

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Preparation of structurally controlled dilute molybdenum-titanium alloys through a novel multi-step internal nitriding technique and their mechanical properties Reviewed

M Nagae, Y Takemoto, T Yoshio, J Takada, Y Hiraoka

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING   406 ( 1-2 )   50 - 56   2005.10

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In order to overcome the recrystallization embrittlement of molybdenum, internally nitrided dilute Mo-Ti alloy specimens having a heavily deformed surface microstructure were prepared by a novel three-step internal nitriding process at 1223-1873 K in N-2 gas. Grain growth behavior and mechanical properties of nitrided specimens were investigated. Primary nitriding of the present alloys below their recrystallization temperature induced a uniform dispersion of ultrafine Ti-nitride precipitates without causing recrystallization. After secondary and tertiary nitriding, those precipitates grew into rod-like particles with a diameter of about 20 nm and a length of 50-120 nm, maintaining their deformed microstructure due to the pinning effect on grain boundary migration. The depth of the region where the recrystallization of the molybdenum matrix was suppressed was greatly dependent on the secondary nitriding temperature. The recrystallization temperature of the specimen subjected to three-step nitriding was elevated above 1873 K. The yield strength at 298 K obtained from nitrided Mo-0.5 wt% Ti alloy was about 1.6 times as high as that of the recrystallized specimen. Ductile-to-brittle transition temperature of nitrided MO-0.5 wt% Ti alloy was about 181 K. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msea.2005.06.039

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Phase transformation of alpha '' martensite structure by aging in Ti-8 mass%Mo alloy Reviewed

Y Mantani, Y Takemoto, M Hida, A Sakakibara, M Tajima

JOURNAL OF THE JAPAN INSTITUTE OF METALS   69 ( 4 )   385 - 391   2005.4

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The orthorhombic alpha" martensite was formed in Ti-8 mass% Mo alloy by quenching from 1223 K. The purpose of this study was to investigate phase transformation of the alpha" martensite structure by isothermal aging. In differential scanning calorimetry curve of the quenched specimen, an exothermic peak that indicated decomposition from the alpha" martensite to a and 8 phases was observed near 780 K, so that isothermal aging was performed at 723 K and 923 K for 9.0 ks. Optical microscopy, X-ray diffraction and transmission electron microscopy were performed to these specimens. Band-like products that were composed of the single variant of omega phase were observed in the quenched alpha" martensite structure. On the other hand, (111)alpha" twins were observed in the 723 K-aged alpha" martensite structure. The quenched alpha" martensite structure indicated low elastic incline and good ductility, whereas the 723 K-aged alpha" martensite structure indicated high yield stress and brittleness. It was pointed out that the omega products were formed to relax the volume expansion from the beta phase to the alpha" martensite, and the (111)alpha" twins were formed during the isothermal aging at 723 K with the extinction of the omega products.

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Ti-8mass%Mo合金におけるα"マルテンサイト組織の時効に伴う相変態 Reviewed

万谷義和,*竹元嘉利,飛田守孝,榊原精,田島守

日本金属学会誌   69巻4号,385頁～391頁   2005

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ω-Phase Product of {112}<111> Twinning Boundary in β-Type Titanium Alloy Reviewed

MANTANI Yoshikazu, TAKEMOTO Yoshito, HIDA Moritaka, SAKAKIBARA Akira

Materia Japan   43 ( 12 )   1020 - 1020   2004.12

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Language：Japanese   Publisher：The Japan Institute of Metals and Materials  

DOI： 10.2320/materia.43.1020

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Heavily Rolled Structure of Ti-Mo Alloy with Non-workhardening Reviewed

TAKEMOTO Yoshito, SAKAKIBARA Akira, SHIMIZU Ichiro

Materia Japan   43 ( 12 )   1026 - 1026   2004.12

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DOI： 10.2320/materia.43.1026

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Phase transformation of alpha '' martensite structure by aging in Ti-8 mass%Mo alloy Reviewed

Y Mantani, Y Takemoto, M Hida, A Sakakibara, M Tajima

MATERIALS TRANSACTIONS   45 ( 5 )   1629 - 1634   2004.5

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The orthorhombic alpha" martensite was formed in Ti-8 mass%Mo alloy by quenching from 1223 K. The purpose of this study was to investigate phase transformation of the alpha" martensite structure by isothermal aging. In differential scanning calorimetry curve of the quenched specimen, an exothermic peak that indicated decomposition from the alpha" martensite to alpha and beta phases was observed near 780K. so that isothermal aging was performed at 723 K and 923 K for 9.0 ks. Optical microscopy, X-ray diffraction and transmission electron microscopy were performed to these specimens. Band-like products that were composed of the single variant of omega phase were observed in the quenched alpha" martensite structure. On the other hand, (1 1 1)alpha" twins were observed in the 723 K-aged alpha" martensite structure. The quenched alpha" martensite structure indicated low elastic incline and good ductility, whereas the 723 K-aged alpha" martensite structure indicated high yield stress and brittleness. It was pointed out that the omega products were formed to relax the volume expansion from the beta phase to the alpha" martensite, and the (1 1 1)alpha" twins were formed during the isothermal aging at 723 K with the extinction of the omega products.

DOI： 10.2320/matertrans.45.1629

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Tensile behavior and cold workability of Ti-Mo alloys Reviewed

Y Takemoto, I Shimizu, A Sakakibara, M Hida, Y Mantani

MATERIALS TRANSACTIONS   45 ( 5 )   1571 - 1576   2004.5

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Three kinds of titanium-molybdenum alloy, Ti-8Mo, Ti-14Mo and Ti-20Mo (mass%), quenched from 1223 K were investigated to clarify the tensile behavior and the cold workability using tensile test and conical cup test. In the quenched state Ti-14Mo showed the superior workability. Ti-20Mo has poor ductility in tensile test, but has relatively good formability in conical cup test. Both Ti-8Mo and Ti-14Mo became brittle through a cold rolling of 50% reduction in thickness; however Ti-20Mo did not change in workability by the cold rolling at all. Hardness remarkably increased with rolling reduction in Ti-8Mo and Ti-14Mo, but was almost constant in Ti-20Mo, especially with Ti-20Mo containing high oxygen. Microstructure of Ti-8Mo and Ti-14Mo rolled until seventy-odd percentage exhibited very fine structure and changed to alpha' + beta and beta structure, respectively. On the other hand Ti-20Mo hardly changed in microstructure by a cold rolling besides the formation of some band-like products. The product was composed of single variant of commensurate omega-phase, whereas the matrix contained four variants of incommensurate omega-phase. It was suggested that the peculiar deformation mechanism of Ti-20Mo was concerned with stress induced transformation of the omega-phase.

DOI： 10.2320/matertrans.45.1571

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An electronic approach to the G.P. zone formation requirement in magnesium and aluminum light metals Reviewed

Moritaka Hida, Kazuo Takao, Akira Sakakibara, Yoshito Takemoto

Keikinzoku/Journal of Japan Institute of Light Metals   54 ( 2 )   62 - 68   2004

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The characteristics in electronic states were investigated by DV-Xα method, which could describe the cluster models for both solid solution (cluster model I) and for G.P. zone (cluster model II) of Mg/Al alloys, Mg-M (M
Al, Ag, Zn) alloys and Al-M (M
Mg, Ag, Zn) alloys. The bond order in the cluster model II for G.P. zone increased more than that in the cluster model I for solid solution in the specific alloy systems where the formation of G.P. zone was detected experimentally. Furthermore, the net charge in the cluster model I for solid solution indicated the significant different characteristics from that in the cluster model II for G.P. zone. By changing the bonding length of each cluster model, the local density of the states around the vicinity of Fermi energy varied high sensitively in FCC cluster models (I and II) of Al-Mg alloy, but not so much in HCP cluster models (I and II) of Mg-Al alloy. The energy gap between HOMO and LUMO was recognized from the consideration of the bond contraction of the cluster model II for G.P. zone, which suggesting the increment in electrical resistance because of the formation of G.P. zone.

DOI： 10.2464/jilm.54.62

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Formation or Extension of {332} 〈113〉 Twin and Commensurate ω Phase during Tensile Deformation in Ti-14 mass%Mo Alloy Reviewed

Yoshikazu Mantani, Yoshito Takemoto, Moritaka Hida, Akira Sakakibara

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals   68 ( 2 )   106 - 109   2004

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The purpose of this study is to investigate the textural changing process and the structural changing process of commensurate ω phase during tensile deformation in the metastable β-type Ti-14 mass%Mo alloy that is formed commensurate ω phase by quench. Optical microscopy, X-ray diffraction and transmission electron microscopy were performed for the specimens that were deformed until different tensile strain. In the 5%-strained specimen, many {332} 〈113〉 twins were formed, and commensurate ω phase of specific variant induced upon tensile deformation. In the 25%-strained specimen, secondary twins or slips which divided early formed {332} 〈113〉 twins into pieces were observed. Fine divided deformation texture was observed in the specimen after fracture, and it is considered that commensurate ω phase changed into incommensurate ω phase or transformed reversely to the β phase. The changing processes of deformation texture and commensurate ω phase were indicated from these results.

DOI： 10.2320/jinstmet.68.106

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Wide range observation on crystal zone of single variant of R-phase and martensite in Ti-50.4 at%Ni alloy Reviewed

Y Takemoto, K Takayama, M Hida, A Sakakibara, J Takada

MATERIALS TRANSACTIONS   44 ( 8 )   1557 - 1561   2003.8

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Wide range selected area electron diffraction (SAD) patterns on &lt;110&gt; crystal-zones (CZ) of a single variant of R-phase in Ti-50.4 at%Ni alloy quenched from 1223 K indicated that the &lt;110&gt; CZs can be classified into two types, CZ-A and CZ-B, with respect to the 1/3&lt;110&gt;* reflections. Especially the absence of 1/3&lt;110&gt;* on the CZ-A could not be explained by the models proposed up to now. Based oil the experimental results, a map that expressed the SAD patterns of single R-phase variant on the ( I I I) stereographic projection was presented. It was suggested that the true structure of R-phase should fulfill three conditions on characteristics of SAD patterns, that is, the reproduction of the unique (111) pattern, the absence of 1/3&lt;110&gt;* reflection at the specific planes on CZ-A and the retainment of three-fold symmetry with respect to the [111]. Bending the TEM sample composed of several R-phase variants caused the integration of the R-phase variants, and resulted in the formation of the B19' martensite. However both the single variant and the B19' martensite returned to the initial state of several R-phase variants after 120 hours at room temperature. It was proposed that the unification of the R-phase variants plays art important role on the R-M transformation.

DOI： 10.2320/matertrans.44.1557

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Effect of WC addition on microstructures of laser melted Ni-based alloy powder Reviewed

YM Zhang, M Hida, A Sakakibara, Y Takemoto

SURFACE & COATINGS TECHNOLOGY   169   384 - 387   2003.6

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Nickel-based alloy powder was laser surface melted on the surface of S45C steel substrate with laser beam. The effect of WC addition on the interface layer and microstructures in laser alloyed layer has been investigated by X-ray diffraction analysis, SEM and TEM. There are three zones in the laser alloyed layer. The interface zone is shown as a bright layer of single gamma-(Fe,Ni) phase. After the addition of WC, the interface changes from flat state to rough state, and the primary arms have smaller cellular structures on the interface. Eutectic of gamma-(Fe,Ni) + Fe23B6 in NiCrBSi sample changes into gamma-(Fe,Ni) + Fe3B in NiCrBSi + 10 wt.% WC sample. In this sample, the eutectic zone approximately 20 mum in width shows fine structure which may be caused by eutectic structure prior growth due to eutectic temperature decrease. The martensite in heat-affected zone is formed due to the decrease of the critical cooling rate. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0257-8972(03)00058-6

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Effecs of Atomization Gas and Heat Treatment on Arc-Sprayed Ti Composite Coatings Reviewed

SAKODA Nobuaki, HIDA Moritaka, SAKAKIBARA Akira, TAKEMOTO Yoshito, TAJIRI Toshiro

Journal of Japan Thermal Spraying Society   40 ( 2 )   52 - 56   2003.4

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Influence of WC addition on microstructures of laser-melted Ni-based alloy coating Reviewed

YM Zhang, M Hida, A Sakakibara, Y Takemoto

JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE   11 ( 6 )   667 - 674   2002.12

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ASM INTERNATIONAL  

Nickel-based alloy powder was surface melted on S45C steel substrate using a CO2 laser. The effect of tungsten carbide (WC) on the interface layer and microstructures in the laser melted layer has been investigated by x-ray diffraction (XRD) analysis, and by scanning and transmission electron microscopy (SEM and TEM) techniques. There are three zones in the laser melted layer: the alloyed zone, the interface zone, and the heat affected zone of substrate. The interface zone appears as a smooth bright layer of single gamma-(Fe, Ni) phase that serves as a primary crystallization phase in the laser alloyed zone. K-S lattice correspondence was recognized between gamma-(Fe, Ni) in the interface and martensite in the substrate. The size of dendritic crystals decreased and eutectic structures in the laser alloyed layer changed after the addition of WC.

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Scanning probe microscopic observation of a surface precipitation of Mg-6 mass%Al alloy Reviewed

Moritaka Hida, Koichi Imada, Akira Sakakibara, Yoshito Takemoto

Keikinzoku/Journal of Japan Institute of Light Metals   52 ( 3 )   126 - 130   2002

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Institute of Light Metals  

Surface and interior precipitations of Mg-6 mass%Al alloy were morphologically studied by SPM observation with AFM and KFM modes, TEM and XRD methods. The hardness increment due to the precipitation was negligibly small. According to AFM contrast the precipitates on the surface were identified as droplet-like particles (1∼4 μ4)
on the other hand the ones formed in the alloy as needle-like (∼1 μm). It was confirmed by XRD that both types of the precipitates had γ-structure (Al12Mg17), and the peak height of the surface precipitates was about 3 times as high as that of the interior ones. The droplet-like precipitates projecting from the surface had a higher KFM electric potential than that of the matrix solid solution, however the precipitates embedded in either the surface layer or the matrix had a lower KFM electric potential.

DOI： 10.2464/jilm.52.126

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Microstructure of alloyed layer and nitriding process in foreign metals under arc sprayed Ti composite coating Reviewed

Nobuaki Sakoda, Moritaka Hida, Yoshito Takemoto, Akira Sakakibara, Toshiro Tajiri

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals   66 ( 12 )   1304 - 1310   2002

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Institute of Metals (JIM)  

We investigated the nitriding process and the microstructure of the alloyed layer between foreign metals under composite arc spraying using two different wire materials, Ti and the paired metal (Mo, Ni, Cu and Al). The Ti element in the composite coatings (Ti-Mo, Ti-Ni, Ti-Cu and Ti-Al) was of TiN and/or TiN0.3, and the oxide or nitride of the paired metal was not found in the coatings. An intermetallic compound (Ti2Al) in the Ti-Al coating was detected in the XRD pattern, but none was detected in the other coatings. It is considered that the reaction of Ti with foreign metal occurs only in the solidification process at the moment of droplet impact. The composite coatings were of very dense packing, and had the diffusion layer in the interface region between the foreign metals. The solute element, Ti in the composite coating Ti-Mo, reacted with nitrogen to form many micrograins of TiN0.3 within molten Mo during thermal spraying. In the other coatings (Ti-Ni, To-Cu and Ti-Al), eutectics were mainly identified, and the Ti nitride in the alloyed layer between foreign metals was only TiN0.3. In addition, the intermetallic compounds, which were not detected in the XRD pattern, were identified in the TEM observation.

DOI： 10.2320/jinstmet1952.66.12_1304

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Formation of α″ martensite and {332} 〈113〉 twin during tensile deformation in Ti-40 mass%Nb alloy Reviewed

Yoshikazu Mantani, Yoshito Takemoto, Moritaka Hida, Akira Sakakibara

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals   66 ( 10 )   1022 - 1029   2002

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The α″ martensite phase in the quenched Ti-40 mass%Nb alloy transforms reversely to the β phase upon short-time aging at 623 K for 0.9 ks, resulting in the β + ω microstructure in the aged specimen. The relationship between the tensile property and the microstructure of this specimen was investigated by the observation of the structural changes in the quenched and aged specimen during tensile deformation. Products of the β phase, which were similar to {332} twins, surrounded by the matrix of α″ martensite were formed in the quenched specimen upon tensile deformation. In the aged specimen, on the other hand, α″ martensites and {332} twins were formed upon tensile deformation. The amount of α″ martensite in the two specimens was larger in the nonuniformly deformed area near the fracture. In particular, concentrated slip occurred in the nonuniformly deformed area of the aged specimen accompanied by the extinction of ω phases. The results indicate that the α″ transformation and then the reverse α″→β transformation were involved in the formation of {332} twins. It is suggested that the formation of {332} twins was due to lattice instability, and that besides the role of deformation resistance, ω phases played a part in nonuniform deformation.

DOI： 10.2320/jinstmet1952.66.10_1022

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Evaluation of bonding state of BCC(Fe) edge dislocation core by DV-X alpha cluster method Reviewed

T Fukuda, M Hida, A Sakakibara, Y Takemoto

MATERIALS TRANSACTIONS   42 ( 11 )   2232 - 2237   2001.11

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

The bonding state has been studied by the discrete variational (DV)-X alpha method in the vicinity of the core of the Peierls-Nabarro edge dislocation in the BCC(Fe) crystal the slip systems of which are {112}&lt; 111 &gt; and {110}&lt; 111 &gt;. Bond order and net charge distribution were evaluated in the perfect crystal model cluster and edge dislocation core model cluster with 32 atoms. In the {112}&lt; 111 &gt; slip system. the total bond order of the nearest neighbor atom pairs in the dislocation model was found to be relatively larger than that in the perfect crystal model. On the other hand, the total bond order of the second neighbor atom pairs in the dislocation model was a little smaller than that in the perfect crystal model. It was also found that there was asymmetry in the bond order between the (110) plane on the left side and the one on the right side of the (110) plane which contains the core atom of dislocation. Net charge and its effect in the dislocation model were larger and wider than those in the perfect crystal model. Almost the same results were also attained for the {110}&lt; 111 &gt; slip system.

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Development of Highly Ductile and Strengthened Mo Alloys due to Recrystallization Control by Multi-step Preferred Nitriding Reviewed

TAKADA Jun, NAGAE Masahiro, HIRAOKA Yutaka, TAKEMOTO Yoshito

Bulletin of the Japan Institute of Metals   40 ( 7 )   666 - 667   2001.7

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DOI： 10.2320/materia.40.666

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Microstructure of a molybdenum nitride layer formed by nitriding molybdenum metal Reviewed

M Nagae, T Yoshio, Y Takemoto, J Takada

JOURNAL OF THE AMERICAN CERAMIC SOCIETY   84 ( 5 )   1175 - 1177   2001.5

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For pure molybdenum nitrided at 1373 K in NH, gas, microstructural observations of a molybdenum nitride layer were conducted through a transmission electron microscope. The molybdenum nitride layer consisted of two molybdenum nitrides: an outer one of gamma -Mo2N and an inner one of beta -Mo2N. A great number of (011)[0(1) over bar 1] type twins were observed in the beta -Mo2N phase, whereas the microstructure of the gamma -Mo2N phase was almost free from lattice defects except for slightly observed (111)(112) type twin.

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An evaluation of bonding states of BCC (Fe) edge dislocation core by DV-Xα cluster method Reviewed

T. Fukuda, M. Hida, A. Sakakibara, Y. Takemoto

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals   65 ( 9 )   852 - 857   2001

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Institute of Metals (JIM)  

Bonding states near the BCC (Fe) edge dislocation core based on the Peierls-Nabarro dislocation model have been studied by discrete variational (DV)-Xα method. The slip systems are {112}〈111〉 and {110}〈111〉. The molecular orbital calculation for the cluster models with 32 atoms belonging to the perfect crystal and Peierls edge dislocation core models were carried out for estimating bond order and net charge distribution among atoms in the cluster models. In {112}〈111〉 slip system total bond order between the nearest neighbor atoms of the dislocation model was found to be larger than that of the perfect crystal model. On the other hand, total bond order of the second neighbor atoms in dislocation model was a little smaller than that in the perfect crystal model. It was also found that there was asymmetry in the bond order between the left side and the right side of the (110) plane which contains the core atom of dislocation. Net charge in the dislocation model was larger than that in the perfect crystal model. Almost the same results were also attained for the {110}〈111〉 slip system.

DOI： 10.2320/jinstmet1952.65.9_852

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Analysis of fine strain field around precipitates using a HOLZ pattern Reviewed

Y Takemoto, M Nagae, M Hida, A Sakakibara, J Takada

JOURNAL OF THE JAPAN INSTITUTE OF METALS   64 ( 5 )   283 - 286   2000

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

Fine strain fields around TiN precipitates in Mo alloys, were analyzed by a newly proposed HOLZ (High Order Laue Zone) pattern method, using transmission electron microscopy. The shape of the TiN precipitates changed into three different types after heat treatment thin plate, rod and sphere. The thin foils for TEM observation were prepared by an electro-polish method. It was found in preliminary experiments using pure Mo that the appropriate condition to obtain a good HOLZ pattern for bcc materials was to choose an orientation which satisfied both low density and uniform distribution of reciprocal spots within the zero order Laue zone. The HOLZ patterns were therefore acquired from the [410] direction of the matrix at room temperature using a convergent electron probe 8.8 nm in diameter operated at 200 kV. Many HOLZ patterns were taken by shooting the electron probe within 150 nm x 150 nm areas that included a precipitate. These patterns were imported into a personal computer using a scanner. It was found that the HOLZ patterns hardly changed its configuration with position but moved as a whole within the center disk depending on position, suggesting lattice rotation of the matrix. The vector maps which indicated the degree and direction of lattice rotation around a precipitate were produced for three types of precipitates. The thin plate of TiN generated a symmetrical mountainous strain field. The rod yielded an asymmetrical valley strain field, and the sphere hardly influenced the matrix. It is considered that the difference in the form of the strain field depending on the shape of precipitate was caused by the degree of coherency between the matrix and the precipitates.

DOI： 10.2320/jinstmet1952.64.5_283

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Deformation induced structural change of quenched ω phase in Ti-20 mass%Mo alloy Reviewed

Yoshikazu Mantani, Yoshito Takemoto, Moritaka Hida, Akira Sakakibara, Kazuyoshi Takayama, Hidehiro Yasuda

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals   64 ( 10 )   934 - 939   2000

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Inst of Metals  

Tensile testing the Ti-20 mass%Mo alloy quenched from 1223 K was performed at 293 K, 623 K and 723 K to investigate the effects quenched ω phase on the mechanical properties. Nominal stress-strain curves after yielding became horizontal with increasing deformation temperature. When deformed at 293 K the dislocation structure observed by TEM had a feature of planner slip concentrated in a banded area. When deformed at elevated temperatures, on the other hand, wavy dislocations were observed to form a cell structure. The specimen deformed after thinning for TEM foil showed the formation of a band product which consisted a single ω-c$/ variant in the vicinity of the crack tip. In situ tensile test in TEM revealed that ω-IC$/ changed into ω-c$/ as deformation progressed. It is considered from these results that deformation behavior at elevated temperatures approached to that of bcc metals because of the stabilization of the β phase, and that the deformation behavior at room temperature was affected by the band product which consists of a single ω-c$/ variant transformed from ω-IC$/. It is further suggested that ω-c$/ can play an obstructing role to the ductility.

DOI： 10.2320/jinstmet1952.64.10_934

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Mechanical properties of molybdenum alloys micro-structurally controlled by internal nitriding Reviewed

M Nagae, J Takada, Y Hiraoka, Y Takemoto, T Yoshio

JOURNAL OF THE JAPAN INSTITUTE OF METALS   64 ( 9 )   751 - 754   2000

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Internally nitrided dilute Mo-Ti alloys having a heavily deformed microstructure near the specimen surface were prepared by a novel two-step nitriding; process at 1173 to 1773 K in N-2 gas. For the nitrided specimens, three-point bend tests were performed at temperatures from 77 to 298 K in order to investigate the effect of microstructure control by internal nitriding on the ductile-brittle transition temperature (DBTT) of the alloy. Yield strength obtained at 243 K of the specimen maintaining the deformed microstructure by the two-step nitriding was about 1.7 times as much as recrystallized specimen. The specimen subjected to the two-step nitriding was bent more than 90 degree at 243 K, whereas recrystallized specimen was fractured after showing a slight ductility at 243 K. DBTT of the specimen subjected to the two-step nitriding and recrystallized specimen was about 153 K and 203 K, respectively. These results indicate that multi-step internal nitriding is very effective to the improvement in the embrittlement by the recrystallization of molybdenum alloys.

DOI： 10.2320/jinstmet1952.64.9_751

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Interface structure in A6061 aluminium alloy matrix composite reinforced with aluminium borate whiskers Reviewed

M Shibata, Y Takemoto

JOURNAL OF THE JAPAN INSTITUTE OF METALS   64 ( 1 )   1 - 6   2000

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

A6061 aluminium alloy matrix composites reinforced with aluminium borate whiskers were manufactured using squeeze casting. The interface between the whisker and matrix was observed using high resolution electron microscopy. The aluminium borate whisker and magnesium in the A6061 aluminium alloy interacted during casting and the spinel (MgAl2O4) which nucleated at the interface grew during heat treatment. The whisker/spinel interface had coherency, but the whisker/matrix interface had none. Many lattice defects were observed in the spinel, and were probably produced by misfits at the whisker/spinel interface. Multi-slice simulation indicated that stacking faults are one of the defects.

DOI： 10.2320/jinstmet1952.64.1_1

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Recrystallization control of dilute molybdenum-titanium alloys by multi-step internal nitriding Reviewed

M Nagae, J Takada, Y Takemoto, Y Hiraoka, T Yoshio

JOURNAL OF THE JAPAN INSTITUTE OF METALS   64 ( 9 )   747 - 750   2000

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The control of microstructure and recrystallization temperature in the internally nitrided dilute Mo-Ti alloys was studied through a novel three-step nitriding process at 900 to 1600 degreesC in Na gas, in order to develop highly ductile Mo alloys having a heavily deformed microstructure near the specimen surface. Primary internal nitriding process below the recrystallization temperature of the present alloys at around 1000 degreesC brings uniform dispersion of superfine Ti-nitride precipitates in the Mo matrix where the deformation microstructure remains. These superfine precipitates decompose and disappear after heating at 1200 degreesC in a vacuum. However, after secondary nitriding at 1500 degreesC in a nitrogen atmosphere, those particles grew up to be stick-shaped particles with a length of 50 to 120 nm without the recrystallization of Mo matrix within about 130 mum from the specimen surface. The depth of the region where the recrystallization of Mo matrix was suppressed was greatly dependent upon the secondary nitriding temperature. The third nitriding was conducted at 1500 or 1600 degreesC. For the specimen nitrided at 1600 degreesC, the recrystallization temperature in a vacuum was elevated above 1600 degreesC.

DOI： 10.2320/jinstmet1952.64.9_747

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Mechanically stimulated reaction of metal/polymer mixed powders Reviewed

Moritaka Hida, Hiroki Iwabu, Akira Sakakibara, Yoshito Takemoto

Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy   46 ( 12 )   1309 - 1314   1999

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Funtai Funmatsu Yakin Kyokai  

Mechanical grinding (MG) with mechanically stimulated reaction was performed on metal/polymer mixed powders. The starting materials used in this study were the metals of Mg, Ti and Mg2Ni powders, and polymer of PTFE, PVC and PE powders. The MG process was investigated using XRD, IR, SEM and TEM. According to XRD results, magnesium fluoride (MgF2, TiF2) and chloride (MgCl2) were detected from MG products of the Mg/PTFE, Ti/PTFE and Mg/PVC blending systems, respectively. Explosive reaction was found during MG of both Mg/PTFE and Ti/PTFE. It was also confirmed by XRD results that the production of MgF2 had already been formed just before the explosive reaction in Mg/PTFE system. It was found from IR analysis that C-C single bond in the polymers, not only both in PTFE and PVC but also in PE, changed to double bond C = C. Hydrogen produced due to decomposition of PE on blending Mg2Ni/PE was absorbed into C-Mg2Ni-H as amorphous solutes. These mechanically stimulated reaction was powerful method for decomposition of engineering plastics.

DOI： 10.2497/jjspm.46.1309

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Nitriding of dilute Mo-Ti alloys at a low temperature of 1373 K Reviewed

M Nagae, S Okada, M Nakanishi, J Takada, Y Hiraoka, Y Takemoto, M Hida, H Kuwahara, MK Yoo

INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS   16 ( 2 )   127 - 132   1998

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

For Mo-0.5 mass% Ti and pure Mo alloy nitrided in a NH3 gas at a relatively low temperature of 1373 K, microstructural observations through optical and transmission electron microscopes, X-ray diffraction analysis and hardness measurements were carried out. A surface nitriding layer with very high hardness of approximately H nu similar to 1800 consisted of two Mo-nitride regions: an outer one of gamma-Mo2N and an inner one of beta-Mo2N. The inward diffusion of nitrogen is a rate-controlling process in the growth of the surface nitriding layer. In Mo-Ti alloy additionally an internal nitriding layer with relatively high hardness of H nu similar to 800 was formed beneath the surface nitriding layer. Such high hardness in the internal nitriding layer was found to result from the uniform dispersion of extremely fine plate-like particles of titanium nitride. The particles are approximately 0.4 nm thick and have coherent strain field in the matrix. (C) 1998 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0263-4368(98)00005-5

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Non-uniform deformation of Fe-3%si alloy single crystals Reviewed

Moritaka Hida, Xiaoping Jiang, Yoshito Takemoto, Kazuaki Yamamoto

Zairyo/Journal of the Society of Materials Science, Japan   47 ( 10 )   1046 - 1052   1998

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Society of Materials Science Japan  

Fe-3%Si alloy single crystals were deformed in tension along the [110] or [001] axis at 77K and 298K in order to study the necking behavior. Two types of deformation band, kink band and band of secondry slip were formed on necking section of specimens deformed at 298K along the [110] or [001] axis, respectively. Cell structure of dislocations in deformed single crystals appeared on the necking section in both axes. Such dislocation structure is supposed to influence non-uniform deformation of the crystals.

DOI： 10.2472/jsms.47.1046

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Comparison of Nitriding Behavior of Mo-Ti Alloys in NH3 and N2 Gases Reviewed

Masahiro Nagae, Akihiro Kunisada, Jun Takada, Yutaka Hiraoka, Yoshito Takemoto, Moritaka Hida, Hideyuki Kuwahara

Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy   45 ( 2 )   189 - 194   1998

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Funtai Funamtsu Yakin Kyokai/Japan Soc. of Powder Metallurgy  

For dilute Mo-Ti alloys and pure Mo nitrided at 1100°C for 16h in NH3 and N2 gases, microstructural observations through optical and transmission electron microscopes, X-ray diffraction analysis and hardness measurements were carried out and the nitriding behavior in N2 and NH3 gases was compared. A surface layer of γ-Mo2N with Hv∼1700 was formed for the nitriding in NH3 gas of 1 atm. In contrast, the surface layer was absent for nitriding in N2 gas at pressures below 10 atm, whereas the β-Mo2N layer was formed at a pressure of 15 atm. In an internal nitriding layer formed beneath the surface layer of Mo-Ti alloys nitrided in NH3 gas, extremely small and plate-like particles of 2∼4nm in width and approximately 0.45nm in thickness were clearly found to precipitate on {100} planes of the matrix. Furthermore, a large coherent strain field was observed in the matrix around each Ti-nitride precipitate. Such a dispersion of the small precipitates resulted in remarkable hardening in the nitrided alloy. The hardness of the internal nitriding layer of the alloys nitrided in NH3 gas was much higher than that in N2 gas. The difference in hardness can be explained in terms of the differences not only in size of the Ti-nitride precipitates but also in their distribution density.

DOI： 10.2497/jjspm.45.189

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Deformation and microstructure of Ti-14Mo alloy in over aged state Reviewed

Y Takemoto, M Hida, A Sakakibara

MATERIALS TRANSACTIONS JIM   38 ( 12 )   1067 - 1071   1997.12

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Deformation and microstructure were investigated on Ti-14 mass%Mo alloy in over aged state using the duplex aging method. In the over aged state only hardness decreased in spire of no change in both size and composition of omega phase. Though the omega phase aged at 623 K for 1 x 10(6) s had the maximum hardness and resulted in the brittle fracture through omega--&gt;beta " transformation, they became soft by over aging and transformed to a phase within the deformation band. The a particles in the band were sheared by {10 (1) over bar 1}(alpha) twinning which direction was perpendicular to the band product. The twinning of alpha particles was regarded as a complementary deformation with volume change in the omega--&gt;alpha transformation. It was suggested that the occurrence of the band product consisted of beta+alpha phases would not be directly connected with brittle fracture.

DOI： 10.2320/matertrans1989.38.1067

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Antiphase domain boundary tubes in plastically deformed Fe-Al alloys with B2 ordered structure Reviewed

ZY Song, M Hida, A Sakakibara, Y Takemoto

SCRIPTA MATERIALIA   37 ( 11 )   1617 - 1622   1997.12

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

DOI： 10.1016/S1359-6462(97)00328-X

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In situ observation of stress-induced martensitic transformation and plastic deformation in TiNi alloy Reviewed

XP Jiang, M Hida, Y Takemoto, A Sakakibara, H Yasuda, H Mori

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING   238 ( 2 )   303 - 308   1997.11

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Stress-induced martensitic transformation and plastic deformation in TiNi alloy have been investigated using transmission electron microscope with an in situ deformation technique. It was found that martensite bands were formed and grew with increasing strain and shrank with decreasing strain in tension. In the second deformation stage, a high density of looped dislocations was formed in the reverse-transformed matrix, while in the first deformation stage dislocations were not formed in the reverse-transformed matrix. The formation of dislocation in the second deformation stage is considered as bearing a relation to reverse martensitic transformation and twinning dislocations lying inside the stress-induced martensite. (C) 1997 Elsevier Science S.A.

DOI： 10.1016/S0921-5093(97)00422-X

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Solid solubility and transformation in mechanically alloyed Ti-Mg powders Reviewed

M Hida, K Asai, Y Takemoto, A Sakakibara

MATERIALS TRANSACTIONS JIM   37 ( 11 )   1679 - 1683   1996.11

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Mechanical alloying (MA) was examined by ball-milling the powder mixtures of various starling compositions, Ti-10, 20, 30, 40, 50, 60, 70, 80, 95 at%Mg plus 2 mass%NaCl powder. NaCl powder was an excellent anti-sticking agent for MA. The process of MA was mainly followed by X-ray diffraction and TEM methods. Super-saturated quasi-solid solution was formed for the samples up to 60 at%Mg. A single hcp structure was newly created up to 30 at%Mg samples, and over this composition range hcp peaks were present in addition to the diffraction pattern which will lead to bcc like nano-crystallite. In the Mg-rich side, Ti-70 similar to 95 at%MA samples showed the coexistence of hcp phases, Ti-based and Mg-based dilute solid solution. The solubility was estimated from the change of lattice constant. But it was somewhat difficult to detect the alloying effect of MA on Mg and Ti in Ti-95 at%Mg sample. MA samples, Ti-20 and -50 at%Mg, showed the starting of phase separation after one hour annealing at 673 and 473 K, respectively.

DOI： 10.2320/matertrans1989.37.1679

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Characterization of glass/steel interfacial zone Reviewed

M Hida, Y Takemoto, ZY Song, M Sawada

JOURNAL OF MATERIALS SCIENCE LETTERS   15 ( 19 )   1669 - 1673   1996.10

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHAPMAN HALL LTD  

DOI： 10.1007/BF00636191

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High-resolution transmission electron microscopic observation of stacking faults in Fe-35 mol%Al alloy with ordered B2 structure Reviewed

ZY Song, M Hida, A Sakakibara, Y Takemoto

MATERIALS TRANSACTIONS JIM   37 ( 2 )   109 - 114   1996.2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

Stacking faults in an Fe-35 mol%Al alloy with the B2 ordered superlattice structure have been investigated by a diffraction contrast method of transmission electron microscopy (TEM). The detailed observation by a phase contrast method of high-resolution transmission electron microscopy (HRTEM) has also been performed on the alloy. Two types of stacking faults were observed by HRTEM. In order to interpret the experimental images, computer simulations of HRTEM images based on different fault models have been carried out. The image simulations reveal that the model of the stacking faults deduced from the diffraction contrast method of TEM (i.e. the displacement vector R = a[100]/2) cannot fit one type of the HRTEM images. In the present study, a possible model of the faults (R = (1 - root 3)a[100]/2) and a mechanism for their production are proposed.

DOI： 10.2320/matertrans1989.37.109

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Effect of phase transformation on localized deformation in Ti-Ni shape memory alloy Reviewed

Xiaoping Jiang, Moritaka Hida, Yoshito Takemoto, Akira Sakakibara, Shuzo Fujii

Zairyo/Journal of the Society of Materials Science, Japan   45 ( 4 )   411 - 416   1996

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Society of Materials Science Japan  

Localized deformation of Ti-50.6at. pct Ni shape memory alloy subjected to tensile loading at different temperatures (≳Af) was studied by means of the observation of internal structure. The rolled sheet specimens were subjected to three types of heat treatments, i.e. annealing at 673K (AC), solution-treatment at 1173K (AQ), and aging at 873K after solution-treatment (AS). It was found AQ and AS specimens that the deformation after the yielding in tensile test was caused by the stress-induced martensite (SIM) transformation, and also by the movement of dislocations which was restricted in martensite bands. The deformation in AQ and AS specimens, therefore, were more localized than in AC specimen where the dislocations were introduced both in the matrix and martensite.

DOI： 10.2472/jsms.45.411

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Martensitic {332}〈113〉 twin in β type Ti-Mo alloy Reviewed

Yoshito Takemoto, Moritaka Hida, Akira Sakakibara

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals   60 ( 11 )   1072 - 1078   1996

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Institute of Metals (JIM)  

The formation mechanism of {332}〈113〉 twin, one of the deformation modes in metastable β type titanium alloys, was examined by high resolution transmission electron microscopy (HR-TEM) and simulation. The interface structure of twin resembled to α″ martensite. Peculiar movement of atoms to form {332}〈113〉 twin was explained by the β→α″ process followed by the α″→β twin inverse transformation process. The former process brought about convenient conditions to form {332}〈113〉 twin
the atom displacement direction was parallel to 〈113〉, habit plane agreed with {332}, shear strain was 0.2907 and volume change was 0.4% expansion. The parameters of α″ obtained by calculation were a=0.3050 nm, b=0.4913 nm and c=0.4596 nm. Subsequently α″→β twin inverse transformation generated by a shear strain of 0.0628 results in {332}〈113〉 twin having a shear strain of 0.3535. It was suggested that atom displacement and compressive stress field with the martensitic transformation would yield a single ω variant or many defects in the twin band.

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HRTEM observation of gradient interface structure of glass/steel joint Reviewed

Moritaka Hida, Yoshito Takemoto, Nobumichi Itatani, Masamitsu Sawada

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals   59 ( 12 )   1273 - 1277   1995

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Inst of Metals  

It has been considered that glass to metal joining is realized by the effects of mechanical anchoring and chemical composition gradient. These effects contribute to prevent glass peeling off caused by the difference in thermal expansion coefficient between glass and metal coupled. In order to clarify these ideas, the interfacial microstructures were studied with a high resolution analytical electron microscope. From the experimental results we found that the interfacial zone was composed of a very complex shape acting as the anchoring effect, and the transitional layer of approx.20 nm in thickness between glass and steel substrate was formed in the layer subjected to the chemical effect. The glass region in the transitional layer with the gradient of the iron component into the glass matrix was kept under the compressive displacement of approx.10%.

DOI： 10.2320/jinstmet1952.59.12_1273

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DEFORMATION-INDUCED TRANSFORMATION OF OMEGA-PHASE IN AGED TI-14 MASS-PERCENT-MO ALLOY Reviewed

Y TAKEMOTO, M HIDA, A SAKAKIBARA

JOURNAL OF THE JAPAN INSTITUTE OF METALS   59 ( 8 )   780 - 787   1995

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

Ti-14 mass%Mo alloys aged for 1x10(6) s at 623 K were deformed by means of a tensile test at 300, 523, 623 and 723 K in Ar atmosphere or of rolling at room temperature in order to investigate the brittle fracture mechanism related to the omega phase. These deformed specimens were observed by optical and transmission electron microscopy. Both deformed structures consisted of many band-like products. In the products, very few omega particles could be found. Instead, zones having a structure different from omega, beta and alpha phases existed. It was found that these zones possessed a body centered triclinic structure, which was newly named beta '' on account of the structural similarity to the beta phase. The beta '' was transformed from omega by deformation. In the transformation process to beta '', one omega variant changed into two types of beta ''; one was closely related to the beta matrix, and the other had a {112}[111] twin relation to the former. It is suggested that the band products act as a path of crack propagation prior to the brittle fracture in the aged Ti-Mo alloy.

DOI： 10.2320/jinstmet1952.59.8_780

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STRUCTURAL STABILITY AND MECHANOCHEMICAL ACTIVITY OF TITANIUM NITRIDE PREPARED BY MECHANICAL ALLOYING Reviewed

WY LIM, M HIDA, A SAKAKIBARA, Y TAKEMOTO, S YOKOMIZO

JOURNAL OF MATERIALS SCIENCE   28 ( 13 )   3463 - 3466   1993.7

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Pure titanium nitride (TiN) was synthesized by mechanical alloying (MA). In order to prevent the contamination from the MA vial and atmospheric gas, the MA steel vial was replaced with a titanium vial and atmospheric gas was deoxidized using sponge titanium heated to 623 K. The mechanochemical activity during MA was estimated from the gas purification temperature. The investigation of thermal and pressure stability by thermal treatment and hot isostatic pressing (HIP) revealed that titanium nitride, TiN, was stable on heating to 1173 K under a vacuum, but became unstable under a high pressure, 100 M Pa.

DOI： 10.1007/BF01159823

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Mechanism of ω→α Transformation in β-Ti Alloy Reviewed

J. Japan Inst. Metals   57 ( 3 )   261 - 267   1993

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DOI： 10.2320/jinstmet1952.57.3_261

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STRUCTURAL RELAXATION OF INTERFACE OF (332) (113) TWIN IN BETA-TI ALLOY Reviewed

Y TAKEMOTO, M HIDA, A SAKAKIBARA

JOURNAL OF THE JAPAN INSTITUTE OF METALS   57 ( 12 )   1471 - 1472   1993

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DOI： 10.2320/jinstmet1952.57.12_1471

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THE DSC AND EXAFS STUDIES OF MECHANICAL AGITATION EFFECTS ON THE LOCAL-STRUCTURE OF SPLAT-COOLED AMORPHOUS NI75SI8B17 ALLOY Reviewed

M HIDA, Y TAKEMOTO, A SAKAKIBARA, H MAEDA

JOURNAL OF NON-CRYSTALLINE SOLIDS   144 ( 2-3 )   196 - 202   1992.7

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Effects of mechanical agitation, extreme cold working, on the structural changes of splat-cooled amorphous alloy were investigated by the differential scanning calorimetry (DSC) and extended X-rav absorption fine structure (EXAFS) methods. The amorphous alloy composed of both matrix and Ni-enriched clusters did not have a detectable endothermic reaction. Since an amorphous alloy agitated by filing did have an endothermic reaction related to a decrease of glass transition temperature as measured by DSC. mechanical agitation has an effect on the structural relaxation and is interpreted with a proposed hierarchy diagram. The filed amorphous phase was changed by milling for 20 h into a chemically homogeneous amorphous state. Further. by milling for 100 h it eventually changed to an amorphous state such as a supercooled liquid matrix with small mean bond distance. Its glass transition temperature, T(g), was decreased to near room temperature. In this state, molecular clusters with large bond distance were separated as a precursor of metastable phase from the supercooled liquid.

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Ti Fiber-Reinforced and Ti Sheet-Enveloped Cast Mg Composite Reviewed

Moritaka Hida, Akira Sakakibara, Yoshito Takemoto, Hiroyuki Okada, Seiji Koga

journal of the japan society of powder and powder metallurgy   39 ( 6 )   464 - 467   1992

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DOI： 10.2497/jjspm.39.464

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DUCTILITY IMPROVEMENT OF TI-MO ALLOY DUE TO TITANIZING Reviewed

Y TAKEMOTO, M HIDA, A SAKAKIBARA, N NISHIDA

JOURNAL OF THE JAPAN INSTITUTE OF METALS   56 ( 5 )   524 - 530   1992

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Diffusion heat-treated Ti-20 mass % Mo (DHT) alloys were prepared by titanizing to improve the ductility, and tested in tension. The DHT alloy had a diffusion layer about 120-mu-m in thickness. The quenched DHT alloy was deformed by twinning in the surface layer and by slip in the interior. Many cracks were generated over the surface of the aged specimen during testing, but the propagation of these cracks were prevented at the interface between the titanized surface layer and the interior. Both the quenched and the aged DHT alloys were elongated well in comparison with non DHT alloys. The formation of diffusion layer in DHT alloy caused a mismatch of deformation modes between the surface layer and the interior.
It was observed using HR-TEM that the growth of omega-particles were remarkably retarded in the interior of aged DHT alloy, and the center of the omega-particle was reversely transformed to beta-phase. It was also found that an unusual fcc phase was formed by the stress induced stacking faults at the interface.

DOI： 10.2320/jinstmet1952.56.5_524

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SOLUTE ENRICHMENT IN THE OMEGA PHASE IN TI-14MO Reviewed

Y TAKEMOTO, M HIDA

SCRIPTA METALLURGICA ET MATERIALIA   25 ( 2 )   299 - 302   1991.2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

DOI： 10.1016/0956-716X(91)90182-Z

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EXAFS AND DIFFRACTION STUDIES OF ATHERMAL AGITATION EFFECTS ON THE LOCAL-STRUCTURE OF AMORPHOUS NI75SI8B17 ALLOY Reviewed

M HIDA, H MAEDA, K KANI, H MORI, A SAKAKIBARA, Y TAKEMOTO

JOURNAL OF NON-CRYSTALLINE SOLIDS   117 ( 118 )   144 - 147   1990.2

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Mechanically Alloyed Ti-Mo Solid Solution and Its Microstructure Reviewed

Woo-Yeong Lim, Moritaka Hida, Akira Sakakibara, Yoshito Takemoto, Hironobu Meada, Eiichi Sukedai

J. Japan Society of Powder and Powder Metallurgy   37 ( 5 )   636 - 639   1990

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Mixture of Ti and Mo powders was mechanically alloyed to obtain β-type Ti-20mass-%Mo alloy. The mechanism of mechanical alloying(MA) of Ti-20mass%Mo and microstructure of its product were investigated by X-ray diffraction, XAFS and TEM. X-ray diffraction profile showed that complete alloying was attained by the 36ks-MA, but incompleteness was revealed by the analysis of XAFS. According to the result of XAFS, 144ks-MA was needed to accomplish alloying. The radial structural parameters of j-th shell, R _j , N _j and σ _j are obtained by curve fitting method on a two-shell, double Mo-Mo and Mo-Ti pairs. Nearest neighbor bond length(R _j ) decreased with the time of MA. From the observation of TEM, it was revealed that mechanically alloyed particle was composed of small domains with different lattice images in direction, like subgrains. Deformation of the lattice image was also recognized for the MA specimen.

DOI： 10.2497/jjspm.37.636

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CHANGE OF DEFORMATION MODE CAUSED BY AGING OF TI-14 MASS-PERCENT MO ALLOY SINGLE-CRYSTALS AND EMBRITTLEMENT MECHANISM DUE TO THE OMEGA-PHASE Reviewed

Y TAKEMOTO, M HIDA, E SUKEDAI, A SAKAKIBARA

JOURNAL OF THE JAPAN INSTITUTE OF METALS   53 ( 10 )   1004 - 1012   1989.10

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DOI： 10.2320/jinstmet1952.53.10_1004

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INFLUENCES OF ENVIRONMENT IN HEAT-TREATMENT AND PRE-AGING AT ROOM-TEMPERATURE ON AGE-HARDENING OF TI-MO ALLOYS Reviewed

M HIDA, E SUKEDAI, Y TAKEMOTO

MATERIALS TRANSACTIONS JIM   30 ( 2 )   102 - 106   1989.2

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DOI： 10.2320/matertrans1989.30.102

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