等通道转角挤压过程中纯铜位错密度变化和力学性能

摘要

The microstructure evolution, dislocation density and mechanical properties of pure copper via equal channel angular pressing were studied to investigate the effects of stack fault energy on the microstructure evolution. The results show that the grain size of annealed pure copper is refined into 5-10 µm, the small grain boundary turns into large ones, subsequently. The dislocation density is 0.16×1014 m-2 after 1 pass and reaches the maximum of 0.41×1014 m-2 after 6 passes, which increases remarkably with increasing the passes. While the recombination and annihilation of dislocations give rise to subsequent density decrease. The tensile strength of annealed copper is 220 MPa with elongation of 53.5%, while the tensile strength reaches 444 MPa and elongation reduces to 22.1%after 8 passes, which reveals that ECPA leads to the improvement of tensile strength and reduction of plasticity. The increased shallow dimple amounts and more uniform distribution of pure copper reveal its ductile fracture mechanism. The results of the microstructure evolution and mechanical property analysis show that, pure copper, as the middle stack fault energy metal material, possesses the characteristic of metal materials with high or low stack fault energy.%利用等通道转角法(Equal channel angular pressing)对纯铜进行挤压变形，研究变形过程中纯铜组织演变，分析位错密度及其相应力学性能变化规律，探讨层错能对组织演变的影响机理。结果表明：退火后纯铜在ECAP变形过程中由小角度晶界逐渐转变为大角度晶界，晶粒尺寸细化到5~10µm；随着挤压道次的增加，纯铜中位错密度显著增大，1道次时位错密度为0.16×1014 m-2，6道次后位错密度达到最大值，为0.41×1014 m-2，之后位错重组和湮灭使得位错密度在一定程度上减小；材料强度明显提高，塑性减小，退火后纯铜的抗拉强度为220 MPa，伸长率为53.5%，8道次后纯铜的抗拉强度为444 MPa，伸长率下降到22.1%；纯铜拉伸断口韧窝数量逐渐增多、变浅且分布均匀，断裂方式整体表现为塑性断裂。通过对组织演化和力学性能分析得出，纯铜作为中等层错能材料，同时具有低层错能和高层错能金属的一些变形特征。