Shape memory effect associated with successive FCC-FCT-BCT martensitic transformation in single-crystalline Fe-Pd alloy

Abstract

Mechanical behaviors under [001] compressive stress have been investigated in an Fe-30.0Pd (at%) alloy, which exhibits successive FCC-FCT-BCT (face-centered cubic, face-centered tetragonal, body-centered tetragonal) martensitic transformation. At 300 K, which is by 10 K above the FCC-FCT transformation temperature, the alloy exhibited a large recoverable strain of 5.7% composed of transformation strain and elastic strain of the FCT phase. The alloy then exhibited stress-induced FCT-BCT transformation. The strain induced by the FCT-BCT transformation was unrecoverable in the stress-removing process, but most of it (90%) recovered when the alloy was heated to 1273 K. The result implies that shape memory effect appears in association with the FCC-FCT-BCT martensitic transformation although the tetragonality (c/a ~ 1.01) of the BCT martensite is the same order as those of Fe-C alloys. Large elastic strain of the FCT phase could be the reason for the shape recovery.