基于等径通道挤压法的超细晶铜动态剪切变形行为实验研究

Experimental Research on Dynamic Shear Behavior of Ultrafine-grained Copper Prepared by Equal Channel Angular Pressing

采用等径通道挤压(ECAP)法制备了超细晶铜,分析其微结构的热稳定性及其对材料动态力学性能的影响。利用Hopkinson压杆及MTS液压伺服实验机对ECAP超细晶铜和原始铜帽型剪切试样进行应变控制加载,结合图像数字相关法及"冻结"回收试样的微观和X射线衍射分析,对其动态剪切变形行为及微观组织演化开展研究。结果表明:ECAP后的超细晶铜在准静态剪切下具有应变硬化特征,但在高应变率下剪切应力-剪切应变曲线呈软化特征;高加载率下产生动态再结晶的绝热剪切带是导致应变硬化率为负的原因;按塑性功计算的超细晶铜再结晶温度仅为325 K,因此超细晶铜在高应变率下易发生绝热剪切失稳变形现象。

The thermal stability of ultra-fine-grained（ UFG） copper microstructure prepared by equal channel angular pressing（ ECAP） method and its influence on the mechanical properties of the material are studied. The Hopkinson pressure bar and MTS hydraulic servo testing machine are used to test ECAP ultrafine grained copper and annealed pure copper samples under strain controlled loading. The evolutions of its dynamic shear deformation behavior and microstructure are studied by digital image correlation method and the microscopic and XRD analysis of ＂frozen＂recovered samples. The test shows that the ECAP UFG copper has strain hardening characteristics under quasi-static shear loading; the shear stressstrain curve presents strain softening characteristics at high strain rate; and the adiabatic shear dynamic recrystallization zone results in strain hardening rate being negative at high loading rate. The recrystalliza-tion temperature of ultrafine grained copper calculated by plastic work is only 325 K. Therefore,the adiabatic shear instability of ultrafine grained copper at high strain rate is easy to occur.