Microstructure and transformation behavior of Ni-Ti-Nb shape memory alloys with low NB content

The structure evolution and phase transformation behavior of Ni-Ti-Nb shape memory alloys with 4.5%Nb (atomic fraction) were studied systematically. It is found that the structure evolution as well as the phase transformation characteristics of the alloys is very sensitive to the ratio of the atomic fractions of Ni and Ti. After appropriate predeformation, a wide hysteresis was observed in such low Nb alloys. The difference of the mechanical behaviors of the alloys with austenite or marten-site states was investigated at the same temperature, and explained by the kinetics of thermoelastic martensitic transformation.