基于软化机制的TC18钛合金本构关系研究

ANALYSIS ON THE CONSTITUTIVE RELATIONSHIP OF TC18 TITANIUM ALLOY BASED ON THE SOFTENING MECHANISM

通过TC18钛合金热模拟压缩实验,得到不同变形条件下的高温变形真应力-真应变曲线.通过加工硬化和动态软化效应,分析变形参数变化对TC18钛合金应力-应变曲线形态和峰值应力的影响.不同变形条件下,TC18钛合金流变曲线呈现出相似的特征,而峰值应力对变形参数的变化却十分敏感.通过Poliak-Jonas准则,分析了不同条件下TC18钛合金在高温变形过程中的软化机制.相同温度下,动态再结晶机制主要发生在低应变速率下的高温变形过程中,并且软化机制的选择对温度不敏感.基于传统的Arrhenius型方程,针对TC18钛合金热变形过程中不同的软化机制,分别建立动态再结晶和动态回复机制下的本构方程.针对识别出的TC18合金在不同变形条件下的软化机制,通过适用的本构模型来描述TC18合金在应变为0.7时真实应力对变形温度、应变速率的响应过程.以动态再结晶为主要软化机制的变形过程,其变形激活能和应变速率敏感系数远远大于以动态回复为主的过程.

The true stress-true strain curves have been attained through the isothermal compression experiment of TC 18 titanium alloy. The influence of deformation parameters on the shape of stress-strain curves and peak stress has been analyzed through the working-hardening and dynamic softening effects. The true stress-true strain curves show the similar characteristics under different deformation conditions. However, the peak stress is sensitive to the changes of deformation parameters. The type of dynamic softening mechanisms in hot deformation under certain conditions can be obtained through Poliak-Jonas criterion. The dynamic recrystallization process tends to take place during the deformation with lower strain rates. And the choice of the dynamic softening mechanisms is not sensitive to deformation temperatures. The suitable constitutive models under different softening mechanisms have been constructed based on the traditional Arrhenius equations. With the identification of the dynamic softening mechanisms in hot deformation of TC18 alloy with different conditions, the response of true stress, at strain of 0.7, to the deformation temperatures and strain rates can be described through the proposed models. And the sensitivity coefficient of strain rates and deformation activation energy, of the process with the dynamic recrystallization as the major softening mechanism, are much larger than the ones of process with dynamic recovery.