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

• Grain size effect on martensitic transformation of Ni50Mn25Ga17Cu8 was revealed.
• The martensitic transformation temperatures were decreased by the smaller grain size.
• The average activation energy of transformation was higher for smaller grains.

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.