Effects of Holding Temperature and Heat Treatment on Microstructure and Properties of TC4 Titanium Alloy Thermal Self-Compressing Bonding Joint

Self-designed induction coils, rigid restraint kits, and the existing laboratory induction heating apparatus were combined to conduct a local induction heating-based rigid restraint thermal self-compressing bonding (TSCB) treatment on a 5 mm-thick TC4 titanium alloy plate (the base metal), and the influence of holding temperature and heat treatment on the microstructure and mechanical properties of the joint was investigated. The results demonstrate that excessively low holding temperature (900 degrees C) results in insufficient atomic diffusion, while excessively high holding temperature (990 degrees C), exceeding the ss. a phase-transition temperature, leads to the formation of coarse Widmanstatten microstructures, both of which contribute to the decrease in the mechanical properties of the joint. As the temperature increases, the pressure applied to the joint by the thermal constraint stress field initially rises and subsequently declines, so does the quality of the joint connection. Optimal mechanical properties are achieved only when the holding temperature is slightly below the ss. a phase-transition temperature, specifically 950 degrees C, at which the microstructure distribution exhibits the highest level of uniformity, characterized by a significant presence of equiaxed a-phase grains. Additionally, the atomic diffusion is sufficiently enhanced, coupled with the highest pressure of the joint exerted by the stress field, resulting in the attainment of optimal mechanical performance. Upon annealing heat treatment at 650 degrees C for 3 h, the a. ss phase-transition is observed, accompanied by a reduction in the degree of lattice distortion and grain refinement. The residual stress state of the TSCB joint transitions from tensile stress to compressive stress. The residual stress is significantly reduced, leading to stress relief. Consequently, the mechanical properties of the TSCB joint are improved, addressing the problem of low plasticity of the TSCB joint.