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385 MPa, 应变率敏感性指数增大至0.021.
Microstructures of commercial purity copper deformed by high-pressure torsion have been examined by means of transmission electron microscopy. Observations have been carried out in two perpendicular directions, i.e. the longitudinal section and the transverse section. Microstructural observations in the longitudinal section revealed a rather different morphology of the dislocation structures from those observed in the transverse section. In the transverse section, dislocation cell structure was formed at low strains. With increasing strain, the dislocation cells continually transformed into equiaxed subgrains and finally into equiaxed grains with high angle grain boundaries due to dynamic recrystallization processes. In the longitudinal section, at low strains, extended dislocation boundaries were observed. With increasing strain, a lamellar structure was observed with some dislocation cell structured across it. The lamellar boundary misorientation as well as the misorentation between the dislocation cells increasing with shear strain. At median strains, the dislocation cells have transformed into elongated subgrains. At large strain, the subgrains transformed into individual grains and the outline of the lamellar structure disappeared. Compression test results show that an increase in yield stress ( 385MPa) and strain rate sensitivity (0.021) as compared to coarse grain copper.
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