IIIrd European Symposium on Martensitic Transformations
ESOMAT'94

J. Phys. IV France 05 (1995) C2-391-C2-396
DOI: 10.1051/jp4:1995260

Influence of Prior Thermomechanical Treatment on the Training Behaviour of a NiTi Alloy

D. Favier¹, Y. Liu² and P.Y. Manach<sup>3

1</sup>  Laboratoire Sols Solides Structures (3S) URA 1511 du CNRS, Université Joseph Fourier, BP. 53X, 38041 Grenoble cedex, France
²  Departement of Mechanical and Materials Engineering, University of Western Australia, Nedlands, W.A. 6009, Australia
³  Laboratoire de Génie Mécanique et Productique, Centre de Génie Industriel Guidel Plages, Université de Bretagne Occidentale, 56520 Guidel, France

Abstract
It is known that two-way memory effect (TWME) can be obtained in shape memory alloys by various types of thermomechanical cycling (training). Although much uncertainty still exists on the physical origin of the TWME, it is well recognised that dislocation arrays developed during training can have an important influence on the TWME. The investigation presented in this paper was designed to provide more information on the influence of initial dislocation structure on the TWME training behaviour of a near equiatomic NiTi alloy. Differences in initial dislocation structure were created by cycling specimens through austenite ←→ martensite transformations in different modes : thermal cycling between 200 K and 370 K, symmetric mechanical cycling to ± 5% shear strain, and combined thermal-mechanical cycling. Subsequent TWME training was performed in tension at a temperature just above Ms by deforming to 5% strain followed by heating. It is found that, whereas the deformation behaviour during training was different for specimens of different prior treatments, the final TWME after training was always the same.

© EDP Sciences 1995