Ti-6Al-2Zr-1Mo-1V合金热变形激活动态再结晶的临界条件识别及表征

An identification and characterization for the dynamic recrystallization critical conditions of Ti-6Al-2Zr-1Mo-1V alloy

热压缩实验获得Ti-6Al-2Zr-1Mo-1V合金在温度1073～1323K,应变速率0.01～10s-1条件下的真应力-应变曲线,以此作为识别及表征动态再结晶临界条件的底层数据。对比分析流变应力曲线发现高温、低应变速率下动态回复型软化态势显著;低温、高应变速率下动态再结晶型软化态势显著。引入材料加工硬化率θ,结合θ-σ曲线拐点判据识别了流变应力曲线隐含表征激活动态再结晶的特征参量:临界应变、临界应力。采用含动态再结晶激活能Q的Arrhenius方程求得α、β、n1、n2等材料常数并获得该合金动态再结晶激活能对应变速率及温度的响应图。进一步引入表征动态再结晶临界条件的临界应变模型,获得了临界应变与各热力参数之间的数学关系,验证表明该临界模型预测精度最大为12.9%。

The true stress-strain curves of Ti-6Al-2Zr-1Mo-1V alloy were achieved by a series of isothermal compression tests under the deformation temperatures 1073-1323K and the strain rates 0.01-10s-1,which would be taken as the basic data for identifying and further characterizing the critical conditions of dynamic recrystallization（DRX）.Through comparison of flow stress curves under different deformation conditions,it＇s found that in low temperature,high strain rate conditions softening effect is mainly due to dynamic recovery,while in high temperature,low strain rate conditions due to dynamic recrystallization.Based on the true stress-strain data,θ-σ curves under different deformation conditions were obtained through introducing hard working rate.Combined with the infection criterion of θ-σ curves,two potential parameters were identified as following： the critical strain and the critical stress for DRX,which contribute to characterizing the initiation of DRX evolution.The Arrhenius equation was introduced for calculating several important material constants such as α,β,n1,n2,and further for response surface of the activation energy of DRX to strain rate and deformation temperature.A critical stain model representing the DRX critical conditions is further adopted and the mathematical relation between critical strain and thermodynamic parameters during hot deformation is explicated.Final results show that the maximum inaccuracy of model is 12.9%.