Grain size effect on the martensitic transformation of Ni₅₀Mn₂₅Ga₁₇Cu₈ high-temperature shape memory alloy

Single crystal, coarse-grained and fine-grained polycrystals of Ni₅₀Mn₂₅Ga₁₇Cu₈ high-temperature shape memory alloy were prepared. Grain size effect on the martensitic transformation was investigated. Compared with the single crystal, the martensitic transformation temperatures were slightly decreased by coarse grains, but were greatly decreased by fine grains. Strong grain size dependence of the kinetics of the martensitic transformation was monitored. The average activation energy of the transformation required for the fine-grained polycrystal was nearly four times of that for the single crystal.