Papers - HAGIHARA Koji
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Temperature and orientation dependence of fracture behavior of directionally solidified duplex-phase crystals composed of Ni(3)X-type intermetallic compounds
Koji Hagihara, Naoyuki Yokotani, Yukichi Urnakoshi
ADVANCED STRUCTURAL AND FUNCTIONAL MATERIALS DESIGN, PROCEEDINGS 512 67 - 72 2006
Language：English Publishing type：Research paper (scientific journal) Publisher：TRANS TECH PUBLICATIONS LTD
Fracture behaviors of three directionally solidified (DS) duplex-phase alloys composed of Ni(3)Nb(D0(a))/Ni(3)Al(Ll(2)), Ni(6)TaAl(D0(24))Ni(3)Al(L1(2)) and Ni(3)Ti(D0(24))/Ni(3)Si(L1(2)) phases, respectively were investigated by three-point bending tests, focusing on temperature and orientation dependence. The temperature-toughness relation showed dissimilar curves depending on alloy. The increasing rate of fracture toughness was the highest in the Ni(3)Al/Ni(3)Nb alloy with fine lamellar structure and was the lowest in the Ni(3)Al/Ni(6)TaAl alloy with rod-like precipitates. The controlling mechanism for the temperature dependence of fracture behavior of Ni(3)Al/Ni(3)Nb alloys was discussed.
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Plastic deformation behavior of NbSi2/MOSi2 crystals with oriented lamellae Reviewed
T. Nakano, K. Hagihara, Y. Nakai, Y. Umakoshi
INTERMETALLICS 14 ( 10-11 ) 1345 - 1350 2006
Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD
Plastic deformation behavior and dislocation microstructure were examined in two-phase silicides with oriented lamellae composed of the C40 (NbSi2) and C11b (MoSi2) phases. (Nb0.15Mo0.85)Si-2 single crystals with the C40 single phase were obtained by a floating zone method, and C11(b) plates precipitated from the C40 matrix during the subsequent annealing at 1400 degrees C satisfying the crystallographic orientation relationship of < <(1)over bar>2 (1) over bar0](C40)//[1 (1) over bar0](C11b) and (0001)(C40)//(110)(C11b). Temperature, annealing time and orientation dependences of plastic deformation behavior in the C40/C11(b) duplex crystals with the strict orientation relationship were examined in compression. Loading axes (phi) were selected to be 0 degrees and 45 degrees from [10 (1) over bar0] on [1 (1) over bar 10] zone in the C40 structure. Yield stress or fracture stress, for example, depended strongly on the angle between the loading axis and lamellar boundaries. The macro-yielding appeared at 1400 degrees C accompanied by the low yield stress around 300 MPa and an adequate plastic strain at phi = 45 degrees, while the crystals deformed at phi = 0 degrees failed just after high fracture stress around 900 MPa showing no plastic flow. This suggests that the deformation proceeds more easily parallel to the lamellar boundaries. In the constituent C11(b) phase, < 100] and 1/2<111] dislocations which are dominantly operative in binary MoSi2 at high temperatures were observed depending on the type of the C11(b) variant. Strain continuity at C11(b)/C11(b) or C11(b)/C40 boundaries was also discussed on the basis of continuity of Burgers vector of operative dislocations. (C) 2006 Elsevier Ltd. All rights reserved.
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Dislocation Structure and Yield Stress Anomaly in D0_<24>-Ni_3Ti Compounds with the GCP Structure Reviewed
HAGIHARA Koji, NAKANO Takayoshi, UMAKOSHI Yukichi
Materia Japan 44 ( 12 ) 997 - 997 2005.12
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Institute of Metals and Materials
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GCP構造を有するDo24型Ni3Ti化合物の転位構造と異常強化挙動
萩原幸司, 中野貴由, 馬越佑吉
特集「電子顕微鏡法による材料開発のための微細構造研究最前線（5）」、まてりあ 2005.12
Language：Japanese Publishing type：Research paper (scientific journal)
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Plastic deformation behavior of Ni3(Ti0.90Nb0.10) single crystals with nine-layered ordered rhombohedral structure Reviewed
K. Hagihara, T. Tanaka, T. Nakano, Y. Umakoshi
Acta Materialia 53 5051 - 5059 2005.10
Publishing type：Research paper (scientific journal)
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Improvement of cyclic oxidation resistance of Y-containing TiAl-based alloys with equiaxial gamma microstructures
Y Wu, K Hagihara, Y Umakoshi
INTERMETALLICS 13 ( 8 ) 879 - 884 2005.08
Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD
The cyclic oxidation behavior of Y-containing TiAl-based alloys was studied by oxidation kinetic curves and microstructural modification of the scale. Oxidation resistance of the experimental alloys in synthetic air at 800 degrees C was improved by Y-addition. The Y-addition was very effective in improvement of the adhesion between scale and alloy due to decrease in thickness of the scale. Diffusion of oxygen and the growth of the oxide grains were strongly impeded by the precipitation of Y2O3 at oxide grain boundaries in the scale which was confirmed by the TEM observation. The excellent oxidation resistance obtained in the Y-containing alloys was mainly attributable to the formation of a continuous Al2O3 scale in the outer layer by retarding inward diffusion of oxygen. (c) 2005 Elsevier Ltd. All rights reserved.
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Crystal structure, phase stability and plastic deformation behavior of Ti-rich Ni-3(Ti,Nb) single crystals with various long-period ordered structures Reviewed
K Hagihara, T Tanaka, T Nakano, Y Umakoshi
Integrative and Interdisciplinary Aspects of Intermetallics 842 91 - 96 2005
Language：English Publishing type：Research paper (international conference proceedings) Publisher：MATERIALS RESEARCH SOCIETY
In Ni-Ti-Nb ternary system, there are some geometrically close-packed (GCP) phases with long-period stacking sequences of a close-packed plane (CPP). Among them, our focus is on the Ni-3(Ti0.90Nb0.10) crystals with Pb3Ba-type rhombohedral structure with nine-fold stacking sequence. Compression tests were conducted using the single crystals and the temperature and orientation dependences of plastic deformation behavior were investigated in comparison with those of D-024-Ni3Ti crystals with the four-fold stacking sequence. The K-W locking of screw dislocation was found to occur not only in the compounds such as Ni3Al and Ni3Ti with a relatively small unit cell, but also even in complex compounds with longer-period stacking structures by slip on the common CPP in the GCP structures.
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Deformation modes and anomalous strengthening of Ni3X-Type intermetallic compounds with the geometrically close-packed structure
Yukichi Umakoshi, Koji Hagihara, Takayoshi Nakano
Materials Science Forum 502 145 - 150 2005
Language：English Publishing type：Research paper (scientific journal)
Plastic deformation behavior including anomalous strengthening of Ni 3X-type compounds with D019, D03 and D0 24 structure were examined and summarized, focusing on the correlation between deformation characteristics and features of their crystal structures.
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Stacking Structure and Phase Stability in Ni-based GCP Compounds Reviewed
HAGIHARA Koji, TANAKA Tetsunori, NAKANO Takayoshi, UMAKOSHI Yukichi
Materia Japan 43 ( 12 ) 993 - 993 2004.12
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Institute of Metals and Materials
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Production of nano-crystal and metallic glass by electron irradiation induced phase transformation.
Takeshi Nagase, Takayoshi Nakano, Hiroyuki Yasuda, Koji Hagihara, Yukichi Umakoshi
2004.10
Language：Japanese Publishing type：Research paper (bulletin of university, research institution)
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Influence of Y-addition on the oxidation behavior of Al-rich gamma-TiAl alloys
Y Wu, K Hagihara, Y Umakoshi
INTERMETALLICS 12 ( 5 ) 519 - 532 2004.05
Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD
Influence of Y-addition on the oxidation behavior of cyclic and isothermal oxidation of Al-rich gamma-TiAl alloys containing 0.1-1.0 at.%Y with equiaxial gamma microstructure was studied in synthetic air with a flow of 200-250 ml/min at 800 degreesC and 900 degreesC. The oxidation rates, structures of scale as well as the scale spallation resistance were closely related to the concentrations of Y. Under isothermal oxidation at 900 degreesC, a small amount of Y-addition (0.1 and 0.3 at.%) was effective in improving the oxidation resistance. especially for 0.3 at.%Y-added sample, which showed suppression of the growth of TiO2 scale, and formation of a protective compact Al2O3 scale at the initial stage of oxidation. However, the alloys with higher Y contents (0.6 and 1.0 at.%) had a detrimental effect on the oxidation resistance after initial isothermal exposure. In the cyclic oxidation tests, all Y-containing alloys showed better oxidation resistance than Y-free alloy oxidized Lit 800 degreesC for 165 h; the Y-containing alloys showed a significantly low weight gain, especially for 0.3 at.%Y-added alloy. The constituents and structures of the multi-layered scale were modified with Y-addition; an additional Y-rich layer composed of fine-grained (Al,Y) O-type oxide was formed close to the TiAl substrate and the formation of continuous Al2O3 scale in the outer layer largely contributed to the improvement of oxidation resistance of TiAl-based alloys. No spallation and cracking were observed at the scale/substrate interface in the higher Y-containing alloys, while Y-free alloy showed severe spallation of the scale at 800 degreesC during cyclic exposure. (C) 2004 Elsevier Ltd. All rights reserved.
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Indentation fracture behavior of (Mo0.85Nb0.15)Si-2 crystals with C40 single-phase and MOSi2(C11(b))/NbSi2(C40) duplex-phase with oriented lamellae Reviewed
K Hagihara, S Maeda, T Nakano, Y Umakoshi
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 5 ( 1-2 ) 11 - 17 2004.01
Language：English Publishing type：Research paper (scientific journal) Publisher：NATL INST MATERIALS SCIENCE
Fracture behavior and toughness of C40-structured (Mo0.85Nb0.15)Si-2 single crystals and MoSi2(C11(b))/NbSi2(C40) duplex-phase crystals with oriented lamellae were investigated by micro-Vickers hardness tests. The indentation fracture toughness in the C40 single-phase showed low values of about 1.0-1.4 MPa m(1/2), while fracture toughness was improved in the duplex-phase crystals. Ductile phase toughening by the C11(b) phase, deflection of crack-propagation at the lamellar boundary and the effect of residual stress field at the crack tip are considered to be responsible for the increment of fracture toughness of MoSi2(C11(b))/NbSi2(C40) duplex-phase crystals. (C) 2003 Elsevier Ltd. All rights reserved.
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Plastic deformation behavior of oriented Ni3Sn crystals with D019 structure Reviewed
K. Hagihara, T. Nakano, Y. Umakoshi
Scripta Materialia 48 577 - 581 2003.11
Publishing type：Research paper (scientific journal)
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Plastic deformation behaviour in Ni3Ti single crystals with D024?structure Reviewed
K. Hagihara, T. Nakano, Y. Umakoshi
Acta Materialia 51 2623 - 2637 2003.10
Publishing type：Research paper (scientific journal)
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Plastic deformation behavior and operative slip systems of ZrSi2 single crystals with C49 type of structure Reviewed
T Nakano, Y Omomoto, K Hagihara, Y Umakoshi
SCRIPTA MATERIALIA 48 ( 9 ) 1307 - 1312 2003.05
Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD
Plastic deformation behavior of ZrSi2 single crystals with C49 type of structure was investigated at temperatures up to 1500 degreesC in comparison with other silicides with C11(b), C40 and C54 types of structures. [100](010), [001](010), [101](010), and [001](100) slip systems were determined to operate and their CRSSs monotonously decreased with increasing temperature. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
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Plastic deformation behavior of Ni3X(X Nb, Ti, Sn) type HCP-based intermetallics with the geometrically close-packed structure Reviewed
K Hagihara, T Nakano, Y Umakoshi
DEFECT PROPERTIES AND RELATED PHENOMENA IN INTERMETALLIC ALLOYS 753 357 - 362 2003
Language：English Publishing type：Research paper (international conference proceedings) Publisher：MATERIALS RESEARCH SOCIETY
In this paper, our recent results on the plastic deformation behaviors of Ni3X-type hcp-based GCP compounds, such as D0(a)-Ni3Nb, D0(19)-Ni3Sn and D0(24)-Ni3Ti, are summarized. The similarity and difference of their plastic behavior are discussed focusing on the correlation with the characteristic features of their crystal structures. The criterion for the occurrence of yield stress anomaly (YSA) by slip on the basal plane is also discussed.
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Slip systems, dislocation structure and plastic deformation behavior of Nl(3)Tl single crystals with D0(24) structure Reviewed
K Hagihara, T Nakano, Y Umakoshi
THERMEC'2003, PTS 1-5 426-4 1709 - 1714 2003
Language：English Publishing type：Research paper (scientific journal) Publisher：TRANS TECH PUBLICATIONS LTD
The plastic deformation behavior of Ni3Ti single crystals with the D0(24) structure was investigated in this study. {1(1) over bar 00}<11(2) over bar 0 > prism slip and (0001)<2(11) over bar 0 > basal slip were operative in Ni3Ti. Anomalous strengthening of yield stress was observed for both slip systems. Especially, a remarkable yield stress anomaly (YSA) was found for the (0001) basal slip system over a wide temperature range between 300 and 800degreesC. The YSA was attributed to the Kear-Wilsdorf locking of 1/3<2(11) over bar 0 > screw dislocations from the (0001) slip plane onto the {01(1) over bar 0} planes.
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Microstructure and compressive flow stress of directionally solidified ternary Ni3(Al, Nb) and quaternary Ni3(Al, Nb, Ti) alloys with duplex phase Reviewed
K. Hagihara, T. Nakano, Y. Umakoshi
Science and Technology of Advanced Materials 3 193 - 199 2002.06
Publishing type：Research paper (scientific journal)
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Effect of Rh and V additions on plastic deformation behaviour in Ni3Nb single crystals with D0a structure Reviewed
Koji Hagihara, Takayoshi Nakano, Yukichi Umakoshi
Materials Transactions 43 ( 9 ) 2267 - 2274 2002
Language：English Publishing type：Research paper (scientific journal) Publisher：Japan Institute of Metals (JIM)
The effect of Rh and V additions on phase stability and plastic deformation behaviour in Ni3Nb single crystals with the D0a structure was investigated, focusing on the slip behaviour of (010)[100], (010)[001] and (001)[100] systems in a wide temperature range between room temperature and 1200°C. The V addition induces no significant change in the critical resolved shear stress (CRSS) for (010)[100] slip at low temperatures, while the Rh addition is effective in increasing the CRSS at temperatures below 500°C and above 800°C, resulting in significant improvement of high-temperature strength. The increment of high-temperature strength is closely related to suppression of the climb motion of edge dislocations. The Rh addition also effectively increases the CRSS for (010)[001] and (001)[100] slip. The V addition was expected to enhance activation of the (010)[001] slip by reducing the SISF energy between the superpartials, but that was not achieved.
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Plastic deformation behavior by slip on (001)[100] in Ni3Nb single crystals with D0a structure Reviewed
K. Hagihara, T. Nakano, Y. Umakoshi
Materials Transactions 42 1998 - 2002 2001.10
Publishing type：Research paper (scientific journal)
