高温变形过程中的动态再结晶类型识别

The identification of dynamic recrystallization type during hot deformation process

通过分析高温变形过程中伴随再结晶晶粒长大的内部位错密度变化,判别不同变形条件下动态再结晶过程的进行形式,研究动态再结晶形式对变形参数的依赖规律,发现：低温大应变速率下,高温变形过程中的再结晶形式以连续性动态再结晶为主;高温低应变速率下,以周期性动态再结晶为主.根据动态再结晶软化与加工硬化平衡,得到反映稳态流动时钛合金流动应力对变形参数的响应,建立具有实际物理意义描述钛合金稳态流动本构关系的Arrhenius型方程.通过热模拟压缩实验得到800~900℃,0.0005~10 s-1条件下的TC18钛合金高温变形流动应力应变曲线,验证动态再结晶形式的判据模型,并通过DMM耗散效率分布图分析模型的适用性.通过显微组织分析,研究不同变形参数下的高温变形过程中,不同动态再结晶形式对应的再结晶晶粒粗化/细化的特点.通过各变形条件下真应变？=0.8时的稳态应力验证得到的本构模型,并分析应变速率敏感系数的变化规律.

The type of dynamic recrystallization process during the high-temperature deformation under different conditions has been identified through the analysis on the dislocation evolution involving with recrystallized grains growing. And the dependence of the type of dynamic recrystallization on the deformation parameters has been discussed. The conditions with lower temperatures and higher strain rates, higher temperatures and lower rates correspond to continuous and periodic DRX, respectively. A constitutive model, describing the response of steady flow stress to deformation parameters, has been proposed based on the balance state of working-hardening and dynamic softening. The constitutive model has a similar type with Arrhenius equation with the coefficients possessing their physical meanings. The true stress-true strain curves during the deformation, with temperatures ranging from 800 to 900℃ and strain rates ranging from 0.0005 to 10 s-1, of TC18 alloy have been obtained through the isothermal compression experiment. The proposed model, identifying the type of dynamic recrystallization, has been verified through the analysis of the flow characteristics of the stress-strain curves under certain deformation conditions. And the power dissipation efficiency map, utilized in DMM model, has been employed to verify the applicability of the model. The correspondence of different types of DRX on the coarsening or refining effect of DRX-ed grains during hot deformation of TC18 alloy has been analyzed through microstructure observation. The proposed constitutive model, suitable to the steady state, has also been verified through substitution of steady stress at strain of 0.8 and the value range of strain rate sensitivity coefficient has been analyzed according to the constitutive model.