Effect of Cu_x substituted for Ga_x on the thermodynamic and fracture behavior in magnetic shape memory Ni₅₀Mn₃₀Ga_{20 − x}Cu_x with high transformation temperature

The effect of Cu_x substituted for Ga_x on the thermodynamic characteristic, evolution of phases and fracture behavior in Ni₅₀Mn₃₀Ga_{20 − x}Cu_x alloys have been investigated. The results show that the martensitic transformation, reverse transformation temperatures and average interface temperature of Ni₅₀Mn₃₀Ga_{20 − x}Cu_x sample increase remarkably with increased content of Cu. The hysteresis temperature of the austenite to martensite transition firstly showed a steep rising trend, then almost reduced to a lower rate with the increased content of Cu up to 4 at.% (the maximum level of copper addition studied). The (202) diffraction peak position was observed to shifted towards high angles, when the Cu content was lower than 1 at.%. Further, the, M₂₀₂ diffraction peak was found to split into two diffraction peaks when the Cu content was more than 1 at.%. In addition, the compressive strength and fracture strain of alloys is clearly enhanced with increased content of Cu. Furthermore, the fracture type of Ni₅₀Mn₃₀Ga_{20 − x}Cu_x alloys was found to changes from intergranular fracture for the Ni–Mn–Ga alloys, to transgranular cleavage fracture with increase in Cu content.