Nb solution influencing on phase transformation temperature of Ni47Ti44Nb9 alloy

The effect of annealing temperature on the phase transformation temperature and microstructure of as-rolled Ni47Ti44Nb9 alloy has been investigated, and the microstructural mechanism has been systematically calculated and analyzed. The results show that annealing treatment elevates phase transformation temperature. With the increase of annealing temperature, Ms temperature increases abruptly below 900 °C, yet above 900 °C, Ms shows no substantial change. Nb gradually dissolves into NiTi matrix, until complete solution at 950 °C. Based on first-principles pseudo-potential plane wave method, a further investigation into micro-mechanism of effect of Nb solution into NiTi(Nb) on the phase transformation temperature is studied by analyzing elasticity modulus and population. Comparing with NiTi matrix, shear modulus c′ and c44 of NiTi(Nb) are rather lower. Following Nb solution into NiTi matrix, Ni-Ti bond is depressed, meanwhile weak Ni-Nb bond and Ti-Nb bond greatly influenced by temperature are formed, as a result of Ms increasing for NiTi(Nb), maybe this is the just micro-mechanism of Nb solution into NiTi alloy.