加热温度和热处理对TC4钛合金热自压连接接头组织和性能的影响

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

采用自行设计的感应线圈、刚性拘束工装与实验室现有感应加热装置结合,以5 mm厚TC4钛合金为母材进行局部感应加热刚性拘束热自压扩散连接(TSCB),探究了不同加热温度和热处理对接头微观组织和力学性能的影响。结果表明,加热温度过低(900℃)会导致原子扩散不充分,加热温度过高(990℃,超过β→α相变温度)会形成的粗大魏氏体组织,导致接头力学性能降低。随着温度的升高,热拘束应力场对接头施加的压力先升高后降低,接头的连接质量也先升高后降低。只有加热温度为950℃即稍低于β→α相变温度时,组织分布最均匀,等轴α相晶粒最明显,且原子扩散更充分,应力场对接头施加的压力最高,接头力学性能最好。经650℃/3 h退火热处理后,发生了α→β相变,晶格的畸变程度降低,晶粒细化。TSCB接头残余应力状态由拉应力转变为压应力。残余应力显著降低,应力得到释放,从而提高了TSCB接头的力学性能,解决了TSCB接头塑性较低的问题。

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°C)results in insufficient atomic diffusion,while excessively high holding temperature(990°C),exceeding theβ→αphase-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 theβ→αphase-transition temperature,specifically 950°C,at which the microstructure distribution exhibits the highest level of uniformity,characterized by a significant presence of equiaxedα-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°C for 3 h,theα→βphase-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.