Orientation Dependence of Plasticity and Fracture in Single-Crystal Superelastic Cu-Al-Mn SMA Bars

The objective of this paper is to examine the orientation dependence of plasticity and fracture in single-crystal superelastic Cu-Al-Mn shape memory alloy (SMA) bars. For this purpose, we prepared 14 single-crystal superelastic Cu-Al-Mn SMA bars of 15-mm diameter and 140-mm length. The crystal orientation was measured using electron backscatter diffraction. This work involved cyclic tension tests up to 10% strain and consecutive monotonic tension tests up to fracture. From these results, strong orientation dependence was observed in plasticity and fracture. Ductility was poor or moderate when the orientation of the specimen was close to the <101> direction. On the other hand, a highly ductile response was observed when the orientation was close to the <112>, <113>, or <001> direction. In these specimens, the fracture strain ranged from 47% to 92%. The large rotation of crystal lattice and the propagation of slip band along the long distance in the longitudinal direction are the reasons for the highly ductile response. Such a highly ductile response is desirable in structural materials, especially in seismic applications for civil structures like buildings and bridges.