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

In the present work we report some results concerning the evolutions of transformation temperatures and microstructure during thermal cycling in Ti47%Ni 3% Co (atomic percent). In the case of hulk material (obtained by a conventional solidification method) high amounts of dislocations l'onn during cycling, which produce a considerable evolution of the transformation temperatures (up LO -40K). wl~i le in mcltspun material containing a dispersion of fine precipitates, the formation 01' 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.