J. Phys. IV France 112 (2003) 1025
DOI: 10.1051/jp4:20031056

Thermomechanical behaviour of FCC HCP martensitic transformation in CoNi

Y. Liu¹, G. Tan¹, S. Miyazaki², Y. Liu³ and B. Jiang<sup>4

1</sup>  Department of Mechanical and Materials Engineering, The University of Western Australia, Crawley, WA 6009, Australia
²  Institute of Materials Science, University of Tsukuba, Ibaraki 305-8573, Japan
³  Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050, China
⁴  Open Laboratory of the Ministry of Education for High-Temperature Materials and Testing, Shanghai Jiao Tong University, Shanghai 200030, China

Abstract
Thermomechanical behaviour of the FCC HCP martensitic transformation in a Co-32wt%Ni single crystal was investigated. The measurement was carried out both by isothermal deformation testing and by heating and cooling under constant load. It was found that the alloy was capable of extensive tensite deformation. Under constant loads, FCC HCP martensitic transformation can be induced on cooling, whereas on heating the reverse transformation from HCP to FCC was induced. This is due to the multiplicity of the reverse transformation, which permits martensite to be further deformed in the direction of the extemal stress to austenite. This behaviour provides a unique case of a negative dependence of the critical transformation temperature on stress, in contrast to conventional thermal shape memory alloys.

© EDP Sciences 2003