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

DOI： 10.2320/matertrans.mt-m2021214

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

DOI： 10.1016/j.tsf.2022.139210

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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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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

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

DOI： 10.2355/tetsutohagane.tetsu-2021-015

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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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Publishing type：Research paper (scientific journal)  

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

DOI： 10.1016/j.tsf.2020.137854

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

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

DOI： 10.2320/matertrans.M2018185

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

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

DOI： 10.2320/jinstmet.J2018013

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

DOI： 10.2320/jinstmet.J2018014

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

DOI： 10.1016/j.jeurceramsoc.2017.03.039

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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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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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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

CiNii Article

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)  

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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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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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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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Language：English   Publishing type：Research paper (international conference proceedings)  

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

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

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

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

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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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Language：English   Publishing type：Research paper (international conference proceedings)  

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

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

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

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

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

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

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

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

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Language：Japanese   Publisher：The Japan Society for Technology of Plasticity  

DOI： 10.9773/sosei.51.410

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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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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

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

DOI： 10.2320/jinstmet.73.752

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

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

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

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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DOI： 10.2320/jinstmet.70.110

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

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

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

DOI： 10.2320/materia.43.1020

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

DOI： 10.2320/materia.43.1026

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

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

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

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

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

DOI： 10.2320/materia.40.666

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CERAMIC SOC  

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

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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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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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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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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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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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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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 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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DOI： 10.1016/S1359-6462(97)00328-X

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

DOI： 10.1007/BF00636191

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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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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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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.

DOI： 10.2320/jinstmet1952.60.11_1072

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

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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DOI： 10.2320/jinstmet1952.57.3_261

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

DOI： 10.2320/jinstmet1952.57.12_1471

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

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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DOI： 10.2497/jjspm.39.464

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

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Language：Japanese   Publisher：Japan Society of Powder and Powder Metallurgy  

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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DOI： 10.2320/jinstmet1952.53.10_1004

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DOI： 10.2320/matertrans1989.30.102

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The changes in mechanical properties and formability of P-type Ti-Mo alloys with Mo content were investigated. Three types of Ti-Mo alloys, Ti-8mass%Mo, Ti-14mass%Mo and Ti-20mass%Mo were prepared, and a monotonic tensile test, a cyclic tensile test and a conical cup drawing test were conducted. It was found that Ti-Mo alloys are superior to Ti6Al4V in cold formability though inferior in tensile strength. Ti-14Mo was found to have excellent deep drawability as well as tensile ductility due to the twin formation. Ti-20Mo, of which the primary deformation mechanism is coarse slip, exhibited inferior tensile ductility but relatively high deep drawability. Ti-8Mo showed intermediate properties concerning cold formability, while it exhibited pseudo elastic type loading-unloading behavior, because of stress induced martensite transformation.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

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In Ti-40mass%Nb alloy quenched from beta phase region, alpha"(orthorhombic) martensite is formed within the beta phase matrix. The a" martensite formed by quenching disappeared by isothermal aging at 623K for 15min, and transformed inversely into beta phase. Change of the structure in quenched specimen and aged one has been investigated by optical microscopy, X-ray diffraction and electron microscopy. Surface relief of alpha" martensite in quenched state was recognized by optical microscope, but could not be recognized after aging. Result of X-ray diffraction indicated that diffraction peaks of alpha" martensite disappeared by aging, and peak intensity of beta phase increased instead. Acicular martensites was observed by SEM and TEM in the quenched state, and many dislocations were observed in the aged state. Tensile tests were performed in quenched specimen and aged one to observe the change of stress-strain curves. The easiness of transformation between alpha" martensite and beta phase is discussed from the microscopic viewpoint.

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New method for analysis of strain field around defect in metals by scanning HOLZ pattern using conventional TEM was proposed. It was able to detect the inclination of lattice plane in the precision of 0.01degrees and to express the figure of strain in the large area. This method was applied to TiN precipitation and dislocation in Molybdenum. Configuration of strain around precipitates varied in their shapes. The plate-shaped precipitate yields symmetric valley like strain, the rod-shaped one generates asymmetric mountain type, and the spherical one hardly raises strain to the matrix. The difference was related to the coherency between precipitates and matrix. There were two kinds of strain field types around dislocations. One was the type of the lattice plane bended by a dislocation, and another was the type showing a spiral vector map around a dislocation. This technique is very simple and is greatly applicable to material research.

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Mechanical alloying(MA) was examined by ball-milling the mixed starting powder of various composition, Ti-10, 20, 30, 40, 50, 60, 70, 80, 95at%Mg plus 2mass%NaCl powder. NaCl powder was an excellent anti-sticking agent for MA. The process of MA was mainly followed by X-ray diffraction method. Super-saturated quasi solid solution was formed for the samples up to 60at%Mg. The single hcp structure was newly created up to 30at%Mg samples, and over this composition range hcp peaks were combined to the diffraction pattern which will lead to bce like nano-crystallite. In Mg rich side, Ti-70 similar to 95at% 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-95at%Mg sample. MA samples, Ti-20 and -50at%Mg, showed the starting of phase separation due to one hour annealing at 673 and 473K, respectively.

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CiNii Books

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Other Link： http://ousar.lib.okayama-u.ac.jp/15489

Language：Japanese   Publisher：岡山大学工学部  

CiNii Article

CiNii Books

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Event date： 2023.2.18

Language：Japanese  

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Event date： 2023.2.18

Language：Japanese  

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Event date： 2023.2.18

Language：Japanese  

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Event date： 2022.12.13

Language：Japanese  

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Event date： 2022.12.13

Language：Japanese  

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Event date： 2022.12.8

Venue：松山  

Event date： 2022.12.8

Presentation type：Oral presentation (invited, special)  

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Event date： 2022.10.22

Venue：新居浜  

Event date： 2022.10.22

Venue：新居浜  

Event date： 2022.10.22

Presentation type：Oral presentation (general)  

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Event date： 2022.10.22

Presentation type：Oral presentation (general)  

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Event date： 2022.9.20 - 2022.9.23

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：仙台  

Event date： 2022.9.20 - 2022.9.23

Presentation type：Oral presentation (general)  

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Event date： 2022.8.23 - 2022.8.24

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鳥取  

Event date： 2022.8.23 - 2022.8.24

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鳥取  

Event date： 2022.8.23

Presentation type：Oral presentation (general)  

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Event date： 2022.7.30

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：香川  

Event date： 2022.7.30

Presentation type：Oral presentation (general)  

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Event date： 2022.2.19

Venue：岡山  

Event date： 2022.2.19

Venue：岡山  

Event date： 2022.2.19

Venue：岡山  

Event date： 2022.2.19

Venue：岡山  

Event date： 2022.2.19

Presentation type：Poster presentation  

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Event date： 2022.2.19

Language：Japanese   Presentation type：Poster presentation  

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Event date： 2022.2.19

Presentation type：Poster presentation  

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Event date： 2022.2.19

Presentation type：Poster presentation  

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Event date： 2022.2.1

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Event date： 2022.2.1

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Event date： 2022.2.1

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Event date： 2022.2.1

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Event date： 2022.2.1

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Event date： 2022.2.1

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：広島（オンライン）  

Event date： 2022.2.1

Language：Japanese   Presentation type：Poster presentation  

Venue：広島（オンライン）  

Event date： 2022.2.1

Language：Japanese   Presentation type：Poster presentation  

Venue：広島（オンライン）  

Event date： 2022.2.1

Language：Japanese   Presentation type：Poster presentation  

Venue：広島（オンライン）  

Event date： 2022.2.1

Language：Japanese   Presentation type：Poster presentation  

Venue：広島（オンライン）  

Event date： 2021.11.3 - 2021.11.6

Language：English   Presentation type：Oral presentation (general)  

Country：Viet Nam  

Event date： 2021.10.9

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2021.9.14 - 2021.9.17

Presentation type：Oral presentation (general)  

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Event date： 2021.9.10 - 2021.9.13

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2021.8.24 - 2021.8.25

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：山口（オンライン）  

Event date： 2021.8.24 - 2021.8.25

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：山口（オンライン）  

Event date： 2021.8.24

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Event date： 2021.3.16 - 2021.3.19

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2020.12.10

Presentation type：Oral presentation (invited, special)  

Venue：オンライン  

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Event date： 2020.12.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

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Event date： 2020.11.25

Presentation type：Oral presentation (invited, special)  

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Event date： 2020.9.9

Presentation type：Oral presentation (general)  

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Event date： 2020.8.24

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2020.8.24

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2020.3.18

Presentation type：Oral presentation (general)  

Venue：東京  

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Event date： 2020.2.15

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山市  

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Event date： 2020.2.15

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山市  

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Event date： 2020.2.15

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山市  

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Event date： 2019.12.4

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：松山市  

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Event date： 2019.11.29

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山市  

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Event date： 2019.11.29

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山市  

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Event date： 2019.11.29

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山市  

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Event date： 2019.11.29

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山市  

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Event date： 2019.11.25

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：岡山市  

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Event date： 2019.9.11 - 2019.9.13

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2019.9.11 - 2019.9.13

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山市  

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Event date： 2019.9.11 - 2019.9.13

Language：Japanese   Presentation type：Poster presentation  

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Event date： 2019.9.11 - 2019.9.13

Language：Japanese   Presentation type：Poster presentation  

Venue：岡山市  

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Event date： 2019.8.19

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2019.8.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山理科大  

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Event date： 2019.8.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山理科大  

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Event date： 2019.8.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山理科大  

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Event date： 2019.2.16

Presentation type：Poster presentation  

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Event date： 2019.2.16

Presentation type：Poster presentation  

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Event date： 2019.2.16

Presentation type：Poster presentation  

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Event date： 2019.2.16

Presentation type：Poster presentation  

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Event date： 2019.2.7

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：鳥取  

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Event date： 2019.1.11 - 2019.1.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京  

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Event date： 2018.12.4

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：高松  

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Event date： 2018.12.4

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2018.9.19 - 2018.9.21

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北大  

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Event date： 2018.9.19 - 2018.9.21

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2018.9.19 - 2018.9.21

Language：Japanese   Presentation type：Poster presentation  

Venue：東北大  

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Event date： 2018.8.20

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2018.8.4

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2018.7.28

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島工大  

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Event date： 2018.6.28 - 2018.6.29

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2018.5.15

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2018.3.19 - 2018.3.21

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2018.3.19 - 2018.3.21

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2018.2.17

Presentation type：Poster presentation  

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Event date： 2018.2.17

Presentation type：Poster presentation  

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Event date： 2018.2.17

Presentation type：Poster presentation  

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Event date： 2018.2.17

Presentation type：Poster presentation  

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Event date： 2017.12.19

Presentation type：Oral presentation (general)  

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Event date： 2017.11.2

Presentation type：Oral presentation (general)  

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Event date： 2017.10.7 - 2017.10.9

Presentation type：Oral presentation (general)  

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Event date： 2017.9.8

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2017.9.6 - 2017.9.8

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2017.9.6 - 2017.9.8

Language：Japanese   Presentation type：Poster presentation  

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Event date： 2017.9.5 - 2017.9.8

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2017.8.28 - 2017.8.30

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2017.8.28 - 2017.8.30

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2017.8.21

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2017.8.21

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2017.7.29 - 2017.7.30

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2017.7.29

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2017.7.29

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2017.2.17

Language：Japanese   Presentation type：Poster presentation  

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Event date： 2017.2.17

Language：Japanese   Presentation type：Poster presentation  

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Event date： 2017.2.17

Language：Japanese   Presentation type：Poster presentation  

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Event date： 2017.2.17

Language：Japanese   Presentation type：Poster presentation  

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Event date： 2017.1.31

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：松山」市  

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Event date： 2017.1.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山市  

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Event date： 2016.12.20

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山市  

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Event date： 2016.11.1 - 2016.11.4

Language：English   Presentation type：Oral presentation (general)  

Venue：ホーチミン  

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Event date： 2016.9.21 - 2016.9.23

Language：Japanese   Presentation type：Poster presentation  

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Event date： 2016.9.21 - 2016.9.23

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2016.9.13 - 2016.9.16

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2016.8.22

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2016.8.1 - 2016.8.5

Language：English   Presentation type：Poster presentation  

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Event date： 2016.8.1 - 2016.8.5

Language：English   Presentation type：Poster presentation  

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Event date： 2016.8.1 - 2016.8.5

Language：English   Presentation type：Poster presentation  

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Event date： 2016.8.1 - 2016.8.5

Language：English   Presentation type：Poster presentation  

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Event date： 2016.7.31

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2016.7.9

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2016.7.9

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2016.7.9

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2016.3.24

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2016.3.24

Language：Japanese   Presentation type：Poster presentation  

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Event date： 2016.3.24

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2016.3.24

Language：Japanese   Presentation type：Poster presentation  

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Event date： 2016.3.24

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2016.2.19

Language：Japanese   Presentation type：Poster presentation  

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Event date： 2016.2.19

Language：Japanese   Presentation type：Poster presentation  

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Event date： 2016.2.19

Language：Japanese   Presentation type：Poster presentation  

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Event date： 2016.2.19

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2016.2.19

Language：Japanese   Presentation type：Poster presentation  

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Event date： 2015.12.18 - 2015.12.20

Language：English   Presentation type：Oral presentation (general)  

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Event date： 2015.11.21 - 2015.11.23

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：横浜  

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Event date： 2015.9.16 - 2015.9.18

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡  

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Event date： 2015.9.16 - 2015.9.18

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡  

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Event date： 2015.9.15

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：札幌  

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Event date： 2015.8.19

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島  

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Event date： 2015.7.4

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山  

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Event date： 2015.7.4

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山  

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Event date： 2015.7.4

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山  

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Event date： 2015.7.4

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山  

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Event date： 2015.7.4

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山  

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Event date： 2015.7.4

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山  

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Event date： 2015.5.22 - 2015.5.24

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2015.3.18

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京  

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Event date： 2015.3.18

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京  

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Event date： 2015.3.18

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京  

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Event date： 2015.3.18

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京  

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Event date： 2015.2.20

Language：Japanese   Presentation type：Poster presentation  

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Event date： 2015.2.20

Language：Japanese   Presentation type：Poster presentation