Effect of annealing on the microstructure and martensitic transformation of magnetic shape memory alloys CoNiGa

A study of the microstructure and martensitic transformation behavior of a new ferromagnetic shape memory Co46Ni27Ga27 alloys at different annealing temperatures (700–1200 °C) and cooling conditions (water quenching, air and furnace cooling) was carried out using optical microscopy (OM), energy dispersive spectrometer (EDS), X-ray diffraction analysis (XRD) and differential scanning calorimeter (DSC). The results show that the wide range starting martensitic transformation temperature Ms, from 40 to 250 °C, increases with annealing temperature and quenching rate, while the precipitation of γ phase was observed in samples conducted with the annealing lower than 1120 °C. At the same time, with decreasing annealing temperature the lattice expansion was determined, which resulted to decrease of Ms.