On the Decrease in Transformation Stress in a Bicrystal Cu-Al-Mn Shape-Memory Alloy during Cyclic Compressive Deformation

The evolution of the inhomogeneous distribution of the transformation stress (ss) and strain fields with an increasing number of cycles in two differently orientated grains is investigated for the first time using a combined technique of digital image correlation and data-driven identification. The theoretical transformation strains (epsilon(T)) of these two grains with crystal orientations [5 3 26](beta) and [6 5 11] fi along the loading direction are 10.1% and 7.1%, respectively. The grain with lower epsilon(T) has a higher ss initially and a faster decrease in ss compared with the grain with higher epsilon(T). The results show that the grains with higher nu(s) might trigger more dislocations during the martensite transformation, and thus result in greater residual strain and a larger decrease in sigma(s) during subsequent cycles. Grain boundary kinking in bicrystal induces an additional decrease in transformation stress. We conclude that a grain with crystal orientation that has high transformation strain and low transformation stress (with respect to loading direction) will exhibit stable transformation stress, and thus lead to higher functional performance in Cu-based shape memory alloys.