Thermoplastic Deformation Behavior And Microstructure Evolvement Of TA15 Titanium Alloy

The characteristics and influence factors of hot deformation behavior of TA15 alloy were investigated. The constitutive equation of flow stress was regressed. Metallography analysis, X-ray diffractometry(XRD) and transmission electron microscopy(TEM) were used to investigate microstructure of the specimens after hot deformation. Rigid-plastic finite element method(FEM) was taken to simulate the strain and bulging in isothermal press experiment. Several geometry models were designed for restricted hot deformation, and all the models had been calculated to compare their features.The results showed that, there exist different hardening and softening tendency in hot compression of TA15 alloy. At 750℃and 1s^-1, the flowing deformation became unstable when compressing ratio reached 60%. At 800℃and 0.001s^-1, TA15 alloy softened with dynamic recrystallization. At 925℃and 0.001s^-1,the deformation exhibited a stable flowing character due to dynamic recovery.Rigid-plastic FEM was conducted to simulate the hot compressing process. The bulging deformation was observed in compressed samples, which was affected by friction factor, strain rate and deformation temperature. The bigger the friction factor, the smaller the strain rate or the lower the deformation temperature, the larger the amount of bulging deformation.Three different geometry models were designed firstly for restricted hot deformation, and then the influence of the different geometry boundaries to the deformation process was analyzed. The primary model was optimized, in which a larger area of homogeneous deformation existed. At last, the forming die of this model was concretely designed.After deforming at 750℃, dislocation slip, dislocation cross slip, tiny metamorphose band and deformation twins were observed. While deformed at 800℃, there were dislocation lines and dislocation loops in initialαphase, and piling up of dislocations at heterophase boundary. Recrystallization was observed inαphase. After deforming at 925℃, there existed dislocation twist, dislocation...