Microstructure and high-temperature shape-memory effect in Ni₅₄Mn₂₅Ga₂₁ alloy

Ni₅₄Mn₂₅Ga₂₁ alloy was prepared to investigate the microstructure, martensitic transformation and high-temperature shape-memory effect. Ni₅₄Mn₂₅Ga₂₁ alloy exhibits single phase of non-modulated martensite with tetragonal structure at room temperature. Its martensitic start temperature M_s, martensitic finish temperature M_f on cooling, and austenitic start temperature A_s, austenitic finish temperature A_f on heating are 260.2, 237.8, 262.5 and 287.8°C, respectively. The compressive strength and strain of Ni₅₄Mn₂₅Ga₂₁ single crystal were measured to be 845 MPa and 20.5%, respectively, with compressive axis along the growth direction of the rods. An excellent shape-memory strain of 6.1%, which is the best performance among high-temperature shape-memory alloys up to the present, is obtained when prestrained to 8%.