高压扭转铜试样的微观组织与压缩性能

通过高压扭转对铜试样施加不同程度的变形，研究了样品扭转面（ND面）和纵截面（TD面）上微观组织特征．对ND面，在较小的剪应变下，原始晶粒形貌模糊，晶粒内部形成等轴状的位错胞及亚晶结构；随变形量的增大，亚晶间取向差及亚晶内部的位错密度增大，最后形成亚微米尺度的等轴晶粒．对TD面，变形初期原始晶粒被拉长，晶粒内部为位错墙分割成的层状结构，层内为拉长的位错胞；随变形程度的增大，拉长晶粒的宽度减小，与剪切方向的夹角减小，晶内层状组织间距减小，并逐渐演化成拉长的亚晶组织；进一步增大变形，晶粒拉长痕迹消失，变形组织与ND面相似，为等轴状亚微米晶粒．压缩实验表明，经16圈扭转后，整个试样上的压缩性能基本均匀，σ0．2达到385MPa，应变率敏感性指数增大至0．021．

Microstructures of the transverse and longitudinal sections of commercial purity copper deformed by high-pressure torsion (HPT) have been examined by OM and TEM. In the transverse section the deformed microstructure is complex, and dislocation cell structures formed in the original grains at low strain levels. With increasing strain, the dislocation cells continuously transformed into equiaxed subgrains and finally into equiaxed grains with high angle grain boundaries. In the longitudinal section the elongated grains with lamellar submicron structures were observed at low strain levels, and with increasing strain the boundary spacing of the elongated grains as well as their orientation angle with respect to the shear direction decreased. In the lamellar structures some elongated dislocation cells formed and the misorientation between them increased with increasing shear strain. At medium strains the elongated dislocation cells transformed into subgrains, which transformed into individual grains at large strain, and the outline of the lamellar structure disappeared. Compression testing results show that the yield stress and strain rate sensitivity of the HPT treated copper reached 385 MPa and 0.021, respectively.