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Effect of Vacancy Clustering on Stabilization of Martensite in Copper Based Shape Memory Alloys

Published online by Cambridge University Press:  25 February 2011

Yingjie Kong ,
Bohong Jiang ,
T.Y. Hsu ,
Baoyi Wang  and
Tianming Wang
Yingjie Kong
Affiliation:
Shanghai Jiao Tong University, Dept. of Materials Science, Shanghai 200030, P.R.China
Bohong Jiang
Affiliation:
Shanghai Jiao Tong University, Dept. of Materials Science, Shanghai 200030, P.R.China
T.Y. Hsu
Affiliation:
Shanghai Jiao Tong University, Dept. of Materials Science, Shanghai 200030, P.R.China
Baoyi Wang
Affiliation:
Lan Zhou University, Dept. of Materials Science, Lan Zhou 730000, P.R.China
Tianming Wang
Affiliation:
Lan Zhou University, Dept. of Materials Science, Lan Zhou 730000, P.R.China
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Abstract

Vacancy behaviors during ageing of Cu-26Zn-4A1 and Cu-14Al-4Ni alloys have been investigated and compared by means of positron annihilation (PA) and electrical resistivity measurement. For ageing in martensitic state after direct quenching, it is observed that the S parameter values of Cu-Zn- Al specimens, measured in liquid nitrogen, increase at first and then decrease, while those of Cu-Al-Ni remain unchanged. The activation energies calculated from the S parameter for increasing and decreasing stages are o.4lev and o.63ev respectively, and the former can be corresponding to the formation energy of vacancy clustering, while the latter may be regarded as the migration energy of effective vacancies. A mechanism is put forward that the clustering of quenched-in vacancies results in a decreasing of the ordering degree and a reduction of the stored energy in martensite, which is responsible for the early stage of the stabilization of martensite in Cu-Zn-Al alloys. However, the fact that Cu-Al-Ni alloy is not subject to the stabilization is assumed to be owing to the immobility of supersaturated vacancies in its martensitic state which may be associated with the strong binding force between Ni and Al atoms.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 246: Symposium M – Shape-Memory Materials and Phenomena--Fundamental Aspects and Applications , 1991 , 25
Copyright
Copyright © Materials Research Society 1992

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