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)高温变形过程中的应力应变行为和组织演变。在400K-500K，应变速率为400K-500K的Al单晶压缩实验中，观察到了流动应力的剧烈波动。第一应力极大值的临界应变10^&lt；-2&gt；s^&lt；-1&gt；-10^&lt；-5&gt；s^&lt；-1&gt；，_c很大程度上取决于试件轴线的晶体取向，其大小依次为&lt；111&>t；，&lt；110&>t；，&lt；在恒定温度下，在某一临界应变速率下，epsilon_c降至最小。用第一应力极大值估算的Al动态再结晶的表观激活能为65kJmol~(-1)~(-1)，与文献报道的Al中大角度晶界运动的激活能很好地一致。Al单晶在…拉伸时的应力-应变曲线较高的773K-873K应变速率的10^&lt；-3&gt；s^&lt；-1&gt；-10^&lt；-5&gt；s^&lt；-1&gt；，没有表现出加工硬化，这表明在恢复过程中发生了动态恢复。在973K-1173K，应变速率为-10^&lt；-5&gt；S^-1&gt；的拉伸条件下，铜单晶继续加工硬化，直到流变应力突然下降到临界点。用X射线Berg-Barrett形貌术对高温变形铝和铜单晶的微观组织进行了分析，发现亚晶由多边形壁和亚晶界组成，沿晶体的拉伸轴方向呈规则分布。Al的亚晶尺寸在稳态时没有明显变化，而在加工硬化阶段，铜的亚晶尺寸显著减小。实验结果表明，试件的尺寸、形状、应力状态以及晶体的层错能和纯度是影响高温回复机制的重要因素。较少

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