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

Abstract

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 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~ile 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.

EBSD studies of microstructure and texture in Ni–Ti–Co shape memory strip and ribbon

“…Recently, unconventional methods of the alloy production, which give possibility of the grain refining and/or their texturing, have been adopted for the SMA. One of them is melt‐spinning or twin roll casting (Pons et al ., 1995; Dalle et al ., 2003; Goryczka et al ., 2004; Goryczka, 2008). Directional heat flow causes that the columnar grains grow in a preferential direction.…”