The microstructure and martensitic transformation of Co–Ni–Ga–Ta ferromagnetic shape memory alloys

The effect of the fourth element Ta on the microstructure, crystal structure and martensitic transformation of (Co 45Ni 25Ga 30) 1− x Ta x ( x = 0, 0.5, 2, 5) alloys was investigated. Some Ta-rich precipitates were observed in the higher Ta-addition samples, which lead to the decrease of the martensitic transformation temperatures and thermal hysteresis. In addition, 1423 K annealing temperature is not high enough to impede the presence of the γ phase in Co–Ni–Ga–Ta alloys, and 1473 K heat treatment temperature is needed.