Preparation and hot compression deformation of biomedical Ni-Ti alloy

A Ti-50. 7% Ni (atomic fraction) shape alloy was prepared by vacuum induction melting under dynamic argon atmosphere. By analyzing the composition, deformation temperature, microstructure, and hardness of the as-cast Ni-Ti shape alloy in this study, it was found that the properties of the as-cast Ni-Ti alloy met the medical standard. To analyze the variation law of the flow stress, the flow stress of the compression deformation for as-cast Ni-Ti alloy was studied by high-temperature compression with a Gleeble-3800 simulated machine within a deformation temperature range of 750-950 ℃, strain rate range of 0. 001-1. 0 s^-1, and strain level of 0. 5. To analyze the relationship between variables in the hot deformation process of as-cast Ni-Ti alloy, a constitutive equation based on dynamic material model was established. To determine the reasonable range of hot working conditions for as-cast Ni-Ti alloy deformation, hot processing maps under different hot deformation conditions were set up. The results show that when the deformation temperature decreases or strain rate increases, the flow stress of as-cast Ni-Ti alloy increases. This phenomenon shows that the main factors affecting the flow stress of as-cast Ni-Ti alloy are deformation temperature and strain rate. When the strain rate is 1. 0 s^-1, the true stress-true strain curves of as-cast Ni-Ti alloy exhibits a zigzag feature. This is mainly attributed to the alternation between hardening and softening during deformation. According to the hot processing maps under different hot deformation conditions, the processing zone and unstable hot deformation region of the as-cast Ni-Ti alloy were obtained. Then, the best temperature range of hot deformation is determined as 820-880 ℃, and the true strain rate is less than 0. 1 s^-1. This study provides a theoretical and data basis for the development of forging process parameters of Ni-Ti alloy.