Faculty Profiles - TAKEMOTO Yoshito

Papers - TAKEMOTO Yoshito

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

M Nagae, T Yoshio, Y Takemoto, J Takada

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

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

M Shibata, Y Takemoto

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

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

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

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

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

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

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

Mechanically stimulated reaction of metal/polymer mixed powders Reviewed

Moritaka Hida, Hiroki Iwabu, Akira Sakakibara, Yoshito Takemoto

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

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

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

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

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

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

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

Moritaka Hida, Xiaoping Jiang, Yoshito Takemoto, Kazuaki Yamamoto

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

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

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

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

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

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

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

Y Takemoto, M Hida, A Sakakibara

MATERIALS TRANSACTIONS JIM 38 ( 12 ) 1067 - 1071 1997.12

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

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-->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-->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

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

ZY Song, M Hida, A Sakakibara, Y Takemoto

SCRIPTA MATERIALIA 37 ( 11 ) 1617 - 1622 1997.12

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

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

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

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

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

DOI： 10.1016/S0921-5093(97)00422-X

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

M Hida, K Asai, Y Takemoto, A Sakakibara

MATERIALS TRANSACTIONS JIM 37 ( 11 ) 1679 - 1683 1996.11

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

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

Characterization of glass/steel interfacial zone Reviewed

M Hida, Y Takemoto, ZY Song, M Sawada

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

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

ZY Song, M Hida, A Sakakibara, Y Takemoto

MATERIALS TRANSACTIONS JIM 37 ( 2 ) 109 - 114 1996.2

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

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

DOI： 10.2320/matertrans1989.37.109

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

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

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

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

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

Yoshito Takemoto, Moritaka Hida, Akira Sakakibara

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

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

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

Moritaka Hida, Yoshito Takemoto, Nobumichi Itatani, Masamitsu Sawada

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

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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