The orientation dependence of transformation strain of Ni–Mn–Ga polycrystalline alloy and its composite with epoxy resin

This study investigated the transformation strains of Ni–Mn–Ga polycrystalline alloy and Ni–Mn–Ga/epoxy resin composites. For the Ni–Mn–Ga polycrystalline alloy, the columnar grains formed along the solidification direction, and the alloy expanded during martensitic transformation in the direction with a transformation strain of ∼500 ppm. For the composite consisting of randomly distributed Ni–Mn–Ga particles, no transformation strain was achieved due to the random distribution of the Ni–Mn–Ga particles. For the composite consisting of properly oriented Ni–Mn–Ga particles, the martensitic transformation strains were found to be orientation-dependent, the shrinking transformation strain-c (parallel to the direction of magnetic field used during curing) up to ∼210 ppm was detected, and the expanding transformation strain-a (vertical to the direction of magnetic field used during curing) was measured to be ∼150 ppm.