Long-Term Microhardness Evolution in Ti-Ni Shape Memory Alloys Processed by Severe Cold Rolling
Ti-50.26at.%Ni shape memory alloy samples were subjected to cold rolling (CR) with true strains encompassing from moderate (logarithmic strain e=0.25) to severe (e=2.1) deformation. СR with e = 0.5 and more initiated a partial austenite amorphization. The evaluation of structural changes in the material during its long-term storage was performed using Vickers microhardness (HV) technique. It was shown that during storage at room temperature up to 9 months, microhardness varied following a dome-shaped trend, thus reflecting commonly encountered interaction between two concurrent time-dependent phenomena, the first responsible for the material hardening, and the second, for the material softening. To represent such phenomena, a simple mathematical model was proposed and experimentally validated.
Yuri Estrin and Hans Jürgen Maier
A. Korotitskiy et al., "Long-Term Microhardness Evolution in Ti-Ni Shape Memory Alloys Processed by Severe Cold Rolling", Materials Science Forum, Vols. 584-586, pp. 1039-1044, 2008