MICROSCOPIC THEORY OF THE SHAPE-MEMORY EFFECT IN TINI

An ab initio study of the Bain strain and orthorhombic distortions in the TiM compounds (M = Ni, Cu, Rh, Pd, and Ag) shows that the B2 struc ture of the shape memory alloy TiNi, unlike that of the other TiM comp ounds, is stable against these distortions, and that TiNi has some fla t total energy minima. A thermodynamic model, built on these findings, displays some features of the shape memory effect. An electronic stru cture analysis reveals the importance of the Ni metallic bonding to th e B2 phase stability and to the detwinning mechanism.