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Relation between Tensile Deformation Behavior and Microstructure in a Ti-Ni-Co Shape Memory Alloy
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Yoichi Kishi1), Zenjiro Yajima1) and Ken’ichi Shimizu1)
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1) AMS R&D Center, Kanazawa Institute of Technology
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Relation between tensile deformation behavior and microstructure in variously aged Ti–49.7 at%Ni–1.3 at%Co shape memory alloys has been investigated. Stress-strain curves for the alloys aged at 623 K and 723 K for 1.8 ks were of a work-hardening type, but those for the alloys aged at the two temperatures over 28.8 ks were nearly of a constant-stress type, as for binary Ti–51 at%Ni aged alloys. Lenticular precipitates were observed in both the 623 K and 723 K aged alloys, and the distance among the precipitates increased with increasing aging temperature and period, as well as the size of the precipitates. The lenticular precipitates were identified to be of the composition of Ti3(Ni, Co)4 from an EDX analysis. Based on these observations, the constant-stress type stress-strain behavior for the alloys aged over 28.8 ks was attributed to some composition change accompanied with the aging progress by which Ti:(Ni+Co) composition ratio in the matrix of the Ti–Ni–Co alloys approached 1:1, as in the equi-atomic Ti–Ni binary alloys.
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Keyword: shape memory alloy, stress-strain behavior, precipitate, transmission electron microscope, martensitic transformation, R-phase
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Received: November 20, 2001
Accepted: March 18, 2002 ,
Published online: September 06, 2005 |
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Copyright (c) 2005 The Japan Institute of Metals |
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