Microstructural Analysis of High Temperature Deformed Al and Cu by X-ray Diffraction Method

研究了面心立方金属（Al和Cu）高温变形的应力-应变行为和显微组织演变。在400 - 500 K，应变速率为10^<-2>s^<-1>-10 ^<-5>s^<-1>的压缩实验中，观察到Al单晶的流变应力有强烈的波动，第一个应力最大值的临界应变ε_c在很大程度上取决于试样轴的晶体学取向，在<111><110><100>恒温条件下，随着应变速率的增加，应变速率的增加。用第一应力极大值估算的Al动态再结晶表观激活能为65 kJ·mol-1<-1>，与文献报道的Al大角度晶界运动激活能一致。 关于我们 773 K-873 K，应变速率10^<-3>s^<-1>-10 ^<-5>s^<-1>，没有表现出加工硬化，表明在恢复过程中发生了动态恢复。Cu单晶在973 - 1173 K、应变速率为-10 s ~ 2的拉伸条件下继续加工硬化<-5>，<-1>直至流变应力在临界点突然下降，用X射线贝格-Barrett形貌术对高温变形的Al和Cu单晶的显微组织进行分析，发现亚晶以晶化壁和亚晶界为边界，沿晶体拉伸轴沿着有规律地分布。亚晶粒尺寸没有明显的变化，观察到在稳定状态下的Al，但相当大的减少，观察到在加工硬化阶段的Cu。Cu晶体在应力骤降后明显地出现了新的再结晶晶粒，实验结果表明，试样的尺寸、形状、应力状态以及晶体的层错能和纯度是影响高温恢复机制的重要因素。少

Stress-strain behavior and microstructural developments in high temperature deformation of fcc metals (Al and Cu) were investigated. Emphasis was on the critical conditions for the occurrence of dynamic recovery and dynamic recrystallization as restoration processes.In the compression tests of Al single crystals, at 400K - 500K with strain rates 10^<-2>s^<-1>-10^<-5>s^<-1>, intense fluctuation of flow stress was observed The critical strain, epsilon_c for the first stress maximum is largely depends on the crystallographic orientation of the specimen axis, in an increasing order of <111>, <110>, <100>.At a constant temperature, epsilon_c decreased to a minimum at a critical strain rate. The apparent activation energy for dynamic recrystallization in Al as estimated by using the first stress maximum is 65kJmol^<-1>, which is in good agreement with the reported activation energy for the motion of high angle grain boundaries in Al.Stress-strain curves for Al single crystals, in tension at … More 773K-873K with strain rates 10^<-3>s^<-1>-10^<-5>s^<-1>, showed no work hardening, suggesting that dynamic recovery is taking place in the restoration process. Cu single crystals continue to work-harden when stressed in tension at 973K-1173K with strain rates -10^<-5>s^<-1>, until the flow stress suddenly drops at a critical point.Microstructure analysis of the high temperature deformed Al and Cu single crystals, by X-ray Berg -Barrett topography, revealed subgrains bordered by polygonization walls and subboundaries, rather regularly distributed along the tensile axis of the crystals. No appreciable change in subgrain size was observed in the steady state for Al, but considerable decrease in size was observed in the work hardening stage for Cu. New recrystallized grains were clearly seen in the Cu crystal after the sudden stress-drop.The present experimrntals results suggest that the size, shape, stress state of specimens, as well as stacking fault energy and purity of the crystals, are the important factors influencing the high temperature restoration mechanisms. Less