Study of Ni–Mn–Ga–Cu as single-phase wide-hysteresis shape memory alloys

Ni50Mn25Ga25−xCux (x = 3–10) alloys were studied as single-phase wide-hysteresis shape memory alloys, with the microstructure, martensitic transformation temperatures and hysteresis, mechanical properties, and shape memory behaviors. Single phase of martensite with tetragonal structure was detected for x < 8, and dual phase containing martensite and the precipitated phase was observed for 8 < x ≤ 10. The martensitic transformation start temperature Ms was linearly increased from 477 K for x = 5 to 673 K for x = 8, then remained constant for x > 9. Simultaneously, the transformation hysteresis As–Ms, between the austenitic start and the martensitic start temperatures, was monotonically expanded from 6.6 K for x = 5 to 40 K for x = 8. The ductility of Ni–Mn–Ga alloys was effectively improved by Cu addition via strengthening the grain boundaries. Shape memory effect of 4.4% was obtained in Ni50Mn25Ga17Cu8 polycrystal. The wide transformation hysteresis, the achieved shape memory effect and the improved ductility indicate Ni–Mn–Ga–Cu alloys a promising candidate for single-phase wide-hysteresis shape memory alloys.

► The transformation hysteresis is expanded by Cu substituting for Ga. ► Cu addition effectively improves the ductility of Ni–Mn–Ga alloys. ► 4.4% shape memory effect is obtained in polycrystalline Ni50Mn25Ga17Cu8.