TEM in situ study of the pre-strained NiTi shape memory alloy—driving force for shape recovery?

The microstructure of pre-strained (4 and 12%) NiTi shape memory alloy (SMA) was studied by using TEM during in situ heating and cooling. It is found that, although both forward and reverse phase transformations have taken place in the TEM samples, the microstructural features of the deformed samples remained identical in both martensite and austenite. The fact that the substructure did not “recover” upon reverse phase transformation seems to suggest that no significant shape recovery has occurred in the observed areas of the TEM samples.