Nb solution influencing on phase transformation temperature of Ni_(47)Ti_(44)Nb_9 alloy

摘要

The effect of annealing temperature on the phase transformation temperature and microstructure of as-rolled Ni_(47)Ti_(44)Nb_9 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, M_s temperature increases abruptly below 900℃, yet above 900℃, M_s shows no substantial change. Nb gradually dissolves into NiTi matrix, until complete solution at 950℃. 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 c_(44) 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 M_s increasing for NiTi(Nb), maybe this is the just micro-mechanism of Nb solution into NiTi alloy.