Faculty Profiles - TAKEMOTO Yoshito

Papers - TAKEMOTO Yoshito

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

Y Takemoto, L Shimizu, A Sakakibara, T Senuma

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

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}< 113 > twin formation. Dynamic observation made clear certain {332}< 113 > 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}< 113 > twin. On the higher content alloys it was found that the stress level on which Young's modulus begins a rise increases with the increase of alloy content. These elastic features were summarized as change of apparent Young's modulus with increase of strain.

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2元系β型チタン合金の変形に伴う弾性挙動変化 Reviewed

竹元嘉利, 清水一郎, 榊原精, 瀬沼武秀

日本金属学会誌 70 ( 2 ) 110 - 113 2006

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

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

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

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

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

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

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

万谷義和,*竹元嘉利,飛田守孝,榊原精,田島守

日本金属学会誌 69巻4号,385頁～391頁 2005

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

MANTANI Yoshikazu, TAKEMOTO Yoshito, HIDA Moritaka, SAKAKIBARA Akira

Materia Japan 43 ( 12 ) 1020 - 1020 2004.12

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

TAKEMOTO Yoshito, SAKAKIBARA Akira, SHIMIZU Ichiro

Materia Japan 43 ( 12 ) 1026 - 1026 2004.12

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

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

MATERIALS TRANSACTIONS 45 ( 5 ) 1629 - 1634 2004.5

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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Tensile behavior and cold workability of Ti-Mo alloys Reviewed

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

MATERIALS TRANSACTIONS 45 ( 5 ) 1571 - 1576 2004.5

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

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

DOI： 10.2320/matertrans.45.1571

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

Moritaka Hida, Kazuo Takao, Akira Sakakibara, Yoshito Takemoto

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

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

Yoshikazu Mantani, Yoshito Takemoto, Moritaka Hida, Akira Sakakibara

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

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

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

MATERIALS TRANSACTIONS 44 ( 8 ) 1557 - 1561 2003.8

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

Wide range selected area electron diffraction (SAD) patterns on <110> crystal-zones (CZ) of a single variant of R-phase in Ti-50.4 at%Ni alloy quenched from 1223 K indicated that the <110> CZs can be classified into two types, CZ-A and CZ-B, with respect to the 1/3<110>* reflections. Especially the absence of 1/3<110>* 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<110>* reflection at the specific planes on CZ-A and the retainment of three-fold symmetry with respect to the [111]. Bending the TEM sample composed of several R-phase variants caused the integration of the R-phase variants, and resulted in the formation of the B19' martensite. However both the single variant and the B19' martensite returned to the initial state of several R-phase variants after 120 hours at room temperature. It was proposed that the unification of the R-phase variants plays art important role on the R-M transformation.

DOI： 10.2320/matertrans.44.1557

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

YM Zhang, M Hida, A Sakakibara, Y Takemoto

SURFACE & COATINGS TECHNOLOGY 169 384 - 387 2003.6

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

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

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

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

YM Zhang, M Hida, A Sakakibara, Y Takemoto

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

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

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

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

Moritaka Hida, Koichi Imada, Akira Sakakibara, Yoshito Takemoto

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

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

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

DOI： 10.2464/jilm.52.126

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

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

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

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

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

DOI： 10.2320/jinstmet1952.66.12_1304

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

Yoshikazu Mantani, Yoshito Takemoto, Moritaka Hida, Akira Sakakibara

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

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

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

DOI： 10.2320/jinstmet1952.66.10_1022

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

T Fukuda, M Hida, A Sakakibara, Y Takemoto

MATERIALS TRANSACTIONS 42 ( 11 ) 2232 - 2237 2001.11

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

The bonding state has been studied by the discrete variational (DV)-X alpha method in the vicinity of the core of the Peierls-Nabarro edge dislocation in the BCC(Fe) crystal the slip systems of which are {112}< 111 > and {110}< 111 >. 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}< 111 > 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}< 111 > slip system.

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

TAKADA Jun, NAGAE Masahiro, HIRAOKA Yutaka, TAKEMOTO Yoshito

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

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Papers - TAKEMOTO Yoshito