金相組織和斷面特征
( 1. 中南大學 材料科學與工程學院, 長沙 410083；
2. 湖南大學 材料科學與工程學院, 長沙 410082)
摘 要: 研究了軸向壓力作用下紫銅棒料塑性剪切分離面附近的微觀組織形態(tài)、剪應變和硬度分布以及剪切分離面形貌。 結果表明： 剪切分離面變形區(qū)可分為3個區(qū)域， 在距表面100~250 μm薄層內， 晶粒發(fā)生了極其劇烈的大剪切塑性變形， 其維氏顯微硬度增大50％； 剪應變隨與剪切分離面距離的增大而減小； 剪切分離面上斷面呈月牙狀， 軸向壓力增大， 斷面減小； 斷面上有大量長條形微孔洞，是由微孔形核后在剪應力作用下沿剪切方向長大和聚合而形成的。
關鍵字: 紫銅棒材；剪切； 微觀組織； 剪切斷裂； 微孔
red copper bar under axial load
LIU Chu-ming1， LIU Wen-li1
（ 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
