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 (Co45Ni25Ga30)1−xTax (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.