IIIrd European Symposium on Martensitic Transformations
ESOMAT'94

J. Phys. IV France 05 (1995) C2-293-C2-298
DOI: 10.1051/jp4:1995245

Study of Dislocations Generated by Thermal Cycling in Ni-Ti-Co Shape Memory Alloys

J. Pons^{1, 2, 3}, L. Jordan^{1, 4}, J.P. Morniroli⁵ and R. Portier<sup>1, 2

1</sup>  Lab. Métallurgie Structurale, ENSCP, 11 rue Pierre et Marie Curie, 75231 Paris cedex 05, France
²  Centre d'Etudes de Chimie Métallurgique, CNRS, 15 rue G. Urbain, 94407 Vitry-sur-Seine, France
³  Dept. de Física, Universitat de les Illes Balears, ctra. de Valldemossa km 7,5, 07071 Palma de Mallorca, Spain
⁴  Faculté de Chirurgie Dentaire, 5 rue Garancière, 75006 Paris cedex 06, France
⁵  Lab. de Métallurgie Physique, Université de Lille I, Bât. C6, 59655 Villeneuve d'Ascq cedex, France

Abstract
In the present work we report some results concerning the evolutions of transformation temperatures and microstructure during thermal cycling in Ti- 47%Ni - 3% Co (atomic percent). In the case of bulk material (obtained by a conventional solidification method) high amounts of dislocations form during cycling, which produce a considerable evolution of the transformation temperatures (up to ~40K), while in meltspun material containing a dispersion of fine precipitates, the formation of dislocations during thermal cycling is highly reduced, giving rise to stable transformation temperatures. The dislocation characteristics have been analysed by means of two-beam condition observations as well as the Large Angle Convergent Beam Electron Diffraction technique. Some energetical considerations concerning the dislocations are pointed out to interpret the evolution of transformation temperatures.

© EDP Sciences 1995