Effect of directional solidification on texture and magnetic-field-induced strain in Ni–Mn–Ga foams with coarse grains

Abstract

Ferromagnetic Ni–Mn–Ga shape memory alloys with large magnetic-field-induced strains are promising candidates for actuators. Here, we cast replicated Ni–Mn–Ga foams with 57vol.% of 355–500μm open pores, with and without directional solidification. The 10M martensitic phase was determined in all foam samples. Directionally solidified foam had a fiber texture, with <100> closely aligned with the solidification direction. In contrast, foams without directional solidification were more randomly textured. One directionally solidified foam showed a maximum magnetic-field-induced strain of 0.65%, which was twice the value displayed by other foams without directional solidification. This improvement is consistent with a reduction in incompatibility stresses between neighboring grains deforming by twinning, generated by a reduction in crystallographic misorientation in textured foam.