Dependence of aging parameters on precipitation behavior, martensitic transformation and mechanical properties of the aged Ni-Ti alloy under super high pressure

The quasi-uniform three-dimensional super high pressure was employed in the Ni-rich Ni-Ti alloy during aging treatment. Moreover, the effects of aging conditions (temperature, time and pressure) on the precipitation of Ti₃Ni₄ phase, martensitic transformation behavior and mechanical properties of the alloy were investigated systematically. The results revealed that the applied of super high pressure can provide the nuclear driving force of Ti₃Ni₄ precipitate and promote the precipitation of Ti₃Ni₄ phase. Unlike the applied of the uniaxial tensile or compressive stress, no significant preferred orientation of Ti₃Ni₄ precipitate was observed in the present stress-assisted aged Ni-Ti alloys as a consequence of the quasi-uniform three-dimensional stress. In addition, a certain number of dislocations generated in the aged Ni-Ti alloys due to the applied of super high pressure. However, the variations of the martensitic transformation behavior and mechanical properties are closely related to the evolution of the precipitation of Ti₃Ni₄ phase with the aging parameters and the generation of internal stress as well as the different thermodynamic state.