金相组织和断面特征
( 1. 中南大学 材料科学与工程学院, 长沙 410083；
2. 湖南大学 材料科学与工程学院, 长沙 410082)
摘 要: 研究了轴向压力作用下紫铜棒料塑性剪切分离面附近的微观组织形态、剪应变和硬度分布以及剪切分离面形貌。 结果表明： 剪切分离面变形区可分为3个区域， 在距表面100~250 μm薄层内， 晶粒发生了极其剧烈的大剪切塑性变形， 其维氏显微硬度增大50％； 剪应变随与剪切分离面距离的增大而减小； 剪切分离面上断面呈月牙状， 轴向压力增大， 断面减小； 断面上有大量长条形微孔洞，是由微孔形核后在剪应力作用下沿剪切方向长大和聚合而形成的。
关键字: 紫铜棒材；剪切； 微观组织； 剪切断裂； 微孔
red copper bar under axial load
（ 1. School of Materials Science and Engineering,
Central South University, Changsha 410083, China;
2. School of Materials Science and Engineering,
Hunan University, Changsha 410082, China）
Abstract: The microstructure, the shear strain and the micro-hardness around the sheared surface by plastic shearing of red copper bar under axial load were examined, and the sheared surfaces were observed by SEM. Three regions with different microstructure features caused by plastic deformation were observed from the sheared surface to the inner matrix. It is shown that the outer surface layer with depth of 100-250 μm endures severely plastic shear deformation during shearing, in which finely equiaxed grains are observed and 50% increase of micro-hardness is detected. The shear strain decreases with the increase of the distance to the sheared surface. The fracture zone takes the shape of crescent symmetrically and its area declines with the increase of the applied axial load. Lots of elongated narrow microvoids along shearing direction are shown in the fractured zone. It is inferred that the fractured zone is formed by the mechanism of nucleation of the microvoids, and then growth and coalescence along the shearing direction.
Key words: red copper bar; shearing; microstructure; shear fracture; microvoid
