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Phase Constitution, Crystal Structures and Hardness of Ti60-xAu40Cox and Ti34-xAu44Co22+x (x=0, 2 and 4) Ternary Alloys

Published online by Cambridge University Press:  26 February 2011

Yasuhito Tsugane ,
Tomonari Inamura ,
Kenji Wakashima  and
Hideki Hosoda
Yasuhito Tsugane
Affiliation:
yasuhito1230@ken.pi.titech.ac.jp, Tokyo Institute of Technology, Graduate School, 259-R2-27 Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan, 81-45-924-5057, 81-45-924-5057
Tomonari Inamura
Affiliation:
inamura.t.aa@m.titech.ac.jp, Tokyo Institute of Technology, Precision and Intelligence Laboratory, 4259 Nagatsuda, Midori-ku, Yokohama, 226-8503 R2-27, Japan
Kenji Wakashima
Affiliation:
wakashima.k.aa@m.titech.ac.jp, Tokyo Institute of Technology, Precision and Intelligence Laboratory, 4259 Nagatsuda, Midori-ku, Yokohama, 226-8503 R2-27, Japan
Hideki Hosoda
Affiliation:
hosoda.h.aa@m.titech.ac.jp, Tokyo Institute of Technology, Precision and Intelligence Laboratory, 4259 Nagatsuda, Midori-ku, Yokohama, 226-8503 R2-27, Japan
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Abstract

It was previously found that two B2 phases (matrix and precipitates) appeared in Ti-32mol%Au-18mol%Co superelastic alloy. In this study, each B2 single phase alloy was tried to be fabricated individually, and phase constitution, crystal structures and hardness were investigated. The chemical compositions were Ti60-xAu40Cox and Ti34-xAu44Co22+x (x=0, 2 and 4), and the alloys were fabricated by Ar-arc melting followed by a hot-forging at 1423K for 43.2ks and a solution treatment at 1173K for 3.6ks. It was found by X-ray diffraction analysis that Ti60-xAu40Cox (called Co-poor alloys) were composed of B19 (Ti, Co)Au and A15 Ti3Au two phases, instead of B2 single phase expected. It was also found that Ti34-xAu44Co22+x (called Co-rich alloys) were composed of C11b Ti(Au,Co)2 and C36 Co2(Ti,Au) two phases, instead of B2 single phase expected. These unexpected phase constitutions appeared in this work may be due to the difference in cooling rate and/or phase transformation from B2 to C11b. Lattice parameters of the obtained phases were precisely determined. The hardness of C11b Ti(Au,Co)2 and C36 Co2(Ti,Au) are HV480 and HV780, respectively. The hardness change of Co-rich alloys can be understood in terms of the volume fraction change of these phases.

Keywords

compoundTix-ray diffraction (XRD)
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 980: Symposium II – Advanced Intermetallic-Based Alloys , 2006 , 0980-II05-51
Copyright
Copyright © Materials Research Society 2007

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References

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