Significant influence of sharp grain boundary corner on tensile elongation of copper bars with columnar grains and its mechanism
(1. School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China;
2. Beijing Laboratory of Metallic Materials and Processing for Modern Transportation, University of Science and Technology Beijing, Beijing 100083, China)
2. Beijing Laboratory of Metallic Materials and Processing for Modern Transportation, University of Science and Technology Beijing, Beijing 100083, China)
Abstract: The reason why elongation of copper bars with columnar grains drops significantly after small cold-drawing was explored. The copper bars were prepared by warm-mould continuous casting. Tensile test was interrupted at various tensile strains in order to detect crack origin. Electron backscattered diffraction (EBSD) was used to analyze dislocation slip bands. It is found that the as-cast microstructure contains sharp grain boundary (GB) corners nearly parallel to the solidification direction (SD). Elongation of the copper bars drops significantly from 68.8% in as-cast state to 18.8% in as-drawn state. It is revealed that plastic deformation becomes severer in the vicinity of sharp GB corners. Locally accumulated internal stress even activates a slip system with very low Schmid factor of 0.17. The localized plastic deformation near sharp grain boundary corner promotes crack initiation and propagation, which eventually leads to the significant drop of elongation.
Key words: copper; fracture; grain boundary corner; elongation; columnar grain