Study on Thermal Deformation Behavior and Microstructure Evolution of TC4 Welded Joint
Based on Gleeble high-temperature tensile test,the thermal deformation behavior of TC4 welded joint was studied under the deformation temperature of 700-950℃and the strain rate of 10-4-10-1 s-1.The thermal deformation constitutive equation of TC4 titanium alloy welded joint was established by using the Arrhenius hyperbolic sine model,and the microstructure evolution of the welded joint in the thermal deformation process was studied by means of optical microscope,SEM and EBSD.The results show that the flow stress of TC4 welded joint is sensitive to the deformation temperature and strain rate,which decreases with the increase of deformation temperature and the decrease of strain rate.The elongation of the welded joint is influenced by the the coupling effect of deformation temperature and strain rate,and increases with the increase of deformation temperature and decrease of strain rate.The deformation activation energy of the welded joint in the(α+β)two-phase area is 547.385 kJ/mol calculated by the constitutive equation,which indicates that the softening mechanism is dynamic recrystallization.With the increase of the deformation temperature,the β-phase content in the weld metal increases,the large angle interface decreases,and the geometrically necessary dislocation density decreases,leading to a decrease in the flow stress of the welded joint and an increase in the elongation.
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