Two-Tier Compatibility of Superelastic Bicrystal Micropillar at Grain Boundary.

Both crystallographic compatibility and grain engineering are super critical to the functionality of shape memory alloys, especially at micro- and nanoscales. Here, we report a bicrystal CuAl24Mn9 micropillar engraved at a high-angle grain boundary (GB) that exhibits enhanced reversibility under very demanding driving stress (about 600 MPa) over 10 000 transformation cycles despite its lattice parameters are far from satisfying any crystallographic compatibility conditions. We propose a new compatibility criterion regarding the GB for textured shape memory alloys, which suggests that the formation of GB compatible twin laminates in neighboring textured grains activates an interlock mechanism, which prevents dislocations from slipping across GB.