超低温等通道转角挤压高导电单晶铜的霍尔佩奇强化

Hall-Petch Strengthening in Single Crystal Copper with High Conductivity During Cryo-ECAP

摘要:

分别采用光学显微镜、扫描电镜、X射线衍射仪和电子背散射衍射分析超低温等通道转角挤压（ECAP）中等应变量单晶铜的形变组织和织构演变，测试材料的力学和导电性能，分析材料组织转变机理及其对材料力学和导电性能的影响。结果表明，超低温ECAP早期形成的定向剪切带在后续变形过程中会严重影响材料组织的转变过程。增加应变量，A路径变形中剪切带内部会形成高密度的位错塞积，特征晶界占比增加；B_C路径变形时剪切带内部的位错发生强烈的交互作用；C路径变形后剪切带的取向发生分散。经过6道次变形后，单晶铜组织中形成强烈的{111}<112>织构，材料强度从初始126.0 MPa增加到400.2 MPa，而导电率仍保持在98%IACS以上。低温ECAP变形后组织内部形成定向剪切带并产生高密度的位错，位错间相互缠结，有效阻碍了位错滑移，而晶粒仍保持良好的单晶特性。

Abstract:

The deformation microstructure and texture evolution of single crystal copper after cryogenic equal channel angular pressing (Cryo-ECAP) process were characterized by optical microscope, scanning electron microscope, X-ray diffractometer, and electron backscatter diffraction. The mechanical properties and conductivity properties were analyzed. The microstructure transition mechanism and its effects on the mechanical properties and conductivity properties were discussed. Results show that the directional shear bands formed in the early stage of Cryo-ECAP process seriously affect the microstructure transformation during the subsequent deformation. With increasing the strain, a high-density dislocation pile-up is formed in the shear bands during deformation by route A, and the proportion of characteristic grain boundaries is increased. The dislocations in the shear bands during deformation by route B_C present strong interactions, and the orientation of shear bands is dispersed after the deformation by route C. After 6 passes of deformation, the strong {111}<112> texture forms in the microstructure of single crystal copper, the strength increases from 126.0 MPa to 400.2 MPa, and the conductivity remains of above 98%IACS. After Cryo-ECAP, the directional shear bands form in the texture and the high-density dislocations are produced. The entanglement of dislocations effectively prevents the dislocation slip, and therefore the grains maintain the characteristics of single crystal.