摘要
In order to analyze the effect of grain size on stress relaxation(SR) mechanism,the SR tests of TC4 alloy with three kinds of grain size were performed in a temperature range of 650-750℃.A modified cubic delay function was used to establish SR model for each grain size.A simplified algorithm was proposed for calculating the deformation activation energy based on classical Arrhenius equation.The grain size distribution and variation were observed by microstructural methods.The experimental results indicate that smaller grains are earlier to reach the relaxation limit at the same temperature due to lower initial stress and faster relaxation rate.The SR limit at 650℃ reduces with decreasing grain size.While the effect of grain size on SR limit is not evident at 700 and 750℃ since the relaxation is fully completed.With the increase of grain size,the deformation activation energy is improved and SR mechanism at 700℃ changes from grain rotation and grain boundary sliding to dislocation movement and dynamic recovery.
为了分析晶粒尺寸对应力松弛机制的影响,对三种晶粒尺寸的TC4钛合金在650~750℃温度范围内进行应力松弛试验。基于一种修改立方延时函数建立每种晶粒尺寸的应力松弛模型。根据经典的Arrhenius方程,提出一种简化算法来计算变形激活能。采用微观手段观察晶粒尺寸分布及变化。实验结果表明,在相同温度下晶粒越细的合金初始应力越小,且松弛速率越快,因而更易达到松弛极限。在650℃,应力松弛极限随晶粒尺寸减小而降低;而在700℃和750℃合金达到完全松弛,导致晶粒尺寸对应力松弛极限影响不显著;随着晶粒尺寸的增大,变形激活能升高,在700℃应力松弛机制从晶粒转动和晶界滑移变换为位错运动和动态回复。
基金
Projects(2016ZE57008,20163657004)supported by Aeronautical Science Foundation of China
Project(USCAST2016-20)supported by the SAST-SJTU Joint Research Centre of Advanced Aerospace Technology,China
Project(51875350)supported by the National Natural Science Foundation of China
