Stress-strain characteristics in Ni-Ga-Fe ferromagnetic shape memory alloys

Tensile and compressive stress-strain characteristics for Ni-Ga-Fe ferromagnetic shape memory alloys at several temperatures were investigated by mechanical test and a critical stress versus temperature diagram was obtained. The crystal structure of the martensite phase obtained by tensile-stress-induced martensitic transformation was estimated from the degree of the transformation strain. Stress-induced martensite transformed from the parent phase with an L2(1) structure showed a 14M structure by tensile stress and by further applying stress, the 14M structure martensitically was transformed into an L1(0) structure. Moreover, it was found in the compressive test that variant rearrangement occurred by very low compressive stress less than 3 MPa, which is similar to the phenomenon seen in Ni-Mn-Ga alloys. (C) 2004 American Institute of Physics.