TB18钛合金热变形行为及动态再结晶机制

High Temperature Deformation Behavior and Dynamic Recrystallization Mechanism of TB18 Titanium Alloy

利用Gleeble 3800热模拟试验机和电子背散射衍射(EBSD)技术研究了TB18钛合金在700~900℃、应变速率0.01~10 s^-1时的热变形行为和动态再结晶机制。研究表明该合金的流动应力大小对应变速率和变形温度敏感。变形初期流动应力皆在达到峰值应力后快速软化,随后有不同程度的上升。通过数据回归得到了该合金在两相区和单相区的高温变形Arrhenius型本构方程,其变形激活能分别为340和185 kJ/mol。其单相区的变形软化机制主要为β相的动态回复,两相区主要为β相的动态再结晶。结合了EBSD技术,金相观察和流变曲线特点的分析表明,在高变形温度,低应变速率时(900℃,0.01 s^-1)主要以几何动态再结晶(GDRX)为主。在温度较低,或变形速率较高下,变形初期发生不连续动态再结晶(DDRX),应变增大后发生连续动态再结晶(CDRX)。

The high temperature deformation behavior and the dynamic recrystallization mechanism of TB18 titanium alloy in the 700℃~900℃range with the strain rate of 0.01~10 s^-1 were studied using the Gleeble 3800 simulator and the electron backscatter diffraction(EBSD)technique.The results show that the value of flow stress of the alloy is sensitive to the strain rate and the deformation temperature.In the initial stage of the deformation,the flow stress will soften rapidly after reaching the peak stress,and then it increases to different levels.The Arrhenius-type constitutive equations of the high temperature deformation of TB18 titanium alloy inα+βboth dual-phase region andβsingle-phase region are obtained through data regression.The apparent activation energy in bothα+βdual-phase region andβsingle-phase region are calculated to be 340 kJ/mol and 185 kJ/mol,respectively.The deformation softening mechanism is mainly controlled by dynamic recrystallization ofβphase inα+βdual-phase region and dynamic recovery ofβphase inβsingle-phase region.According to the EBSD maps,the metallographic observation and the characteristics of stress-strain curves,it is concluded that the geometric dynamic recrystallization(GDRX)prevails when the deformation is conducted at high temperature and low strain rate(900℃,0.01 s^-1).As the lower temperature or the higher strain rate is applied,the discontinuous dynamic recrystallization(DDRX)takes place at the initial stage of the deformation and the continuous dynamic recrystallization(CDRX)is shown after the strain increases.