单晶铜拉拔过程组织及织构演变

Evolution of Microstructure and Texture in Drawn Single Crystal Copper

目的通过分析单晶铜线材在冷拉拔过程中不同位置微观结构的变化情况,得到变形过程中组织及织构的演变规律。方法采用冷型下引连铸装置制备得到ϕ8 mm高纯铜铸态杆坯,并在大拉机中进行多道次拉拔,获得了真应变分别为0.5、1.3、2、2.7和3.4的铜线样品;采用电子背散射衍射技术分别对铸态及拉拔态试样纵截面的显微组织以及织构进行观测。结果拉拔开始后,在试样纵截面上部的次表层率先观察到与轴向呈45°的滑移带,试样下部开始分裂出平行于拉拔方向的柱状晶。随着应变的增加,位于次表层的滑移线数目显著增多,滑移带间距更加紧密,随后在试样芯部也观察到与轴向呈30°的滑移带,试样边部晶粒的裂化程度更加显著,形成大量平行于轴向的纤维晶粒。当真应变增加至3.4时,少量倾斜于轴向的晶粒在外力作用下被拉至与轴向平行,最终形成致密的纤维组织。在整个拉拔过程中,铜线纵截面上下2个边部由初始的<001>织构先后演化出<114>、<112>、<433>、<111>织构,芯部演化出<112>、<111>织构。结论在拉拔过程中,不同位置的变形程度不同,组织及织构的演变也表现出较为明显的差异。总体表现为,线材边部比芯部变形程度更加剧烈,组织纤维化程度更高,织构演变也更加复杂。

The work aims to understand the evolution of the structure and texture during deformation by analyzing the microstructural changes in single crystal copper wires at different positions during cold drawing.The high-purity copper cast rod billet with a diameter of 8 mm was prepared with the vacuum downward continuous casting equipment.It was drawn through a large drawing machine for several passes to obtain copper wire samples with true strains of 0.5,1.3,2,2.7,and 3.4.The microstructure in the longitudinal sections of cast and drawn specimens,as well as their grain orientations,were observed using the EBSD(Electron Backscattered Diffraction)technique.The results showed that after the start of drawing,the sub-surface layer near the upper part of single-crystal copper first formed a slip band at 45°to the axial direction,and the lower part of the columnar crystals became parallel to the direction of drawing.As the strain increased,the number of slip lines located in the subsurface layer increased significantly,the slip bands got more closely spaced.Subsequently,the slip bands at 30°to the axial direction appeared in the core of the specimen,and the cracking of the grains at the edge of the specimen became more pronounced,resulting in the formation of a large number of fibrous grains that were parallel to the axial direction.When the true strain reached 3.4,a small number of tilted grains were pulled parallel to the axial direction by the external force,and finally a dense fibrous structure was formed.During the whole drawing process,the surface texture of the copper wire in the longitudinal section evolved successively from the initial<001>orientation to<114>,<112>,<433>,<111>,with<112>and<111>orientations developing in the center.During the drawing process,the degree of deformation varies at different locations,resulting in distinct differences in the evolution of structure and texture.Generally,the surface of the wire undergoes more intense deformation than the center,resulting in a more fibrous structure and more complex texture evolution.