Bulk processing of fine grained OFHC copper by cyclic channel die compression

Abstract

Abstract The applicability of cyclic channel die compression (CCDC) for producing fine grained structure in oxygen free high conductivity (OFHC) copper is investigated in the present work. OFHC copper was severely plastically deformed at room temperature up to an effective plastic strain of 7.2 through three cycles of CCDC. Optical microscopy studies indicated microstructural inhomogeneity after the first cycle followed by considerable improvements in deformation homogeneity during subsequent straining. EBSD analysis of microstructural evolution revealed maximum grain refinement during the initial stages of strainitrun 2176 ng and lower grain refinement rates subsequently. Substantial grain refinement in CCDC processed samples was manifested by the formation of fine grained equiaxed structures (∼1 – 2 μm) from coarse grained (58 μm) starting material after three cycles. Grain boundary characteristics divulged continuous changes in the relative fraction of high-angle and low-angle boundaries with strain. The room temperature tensile behaviour indicated considerable improvement in yield strength by ∼3.5 times from 129 MPa to 422 MPa after the first cycle correlating with the structural refinement observed. Initially degraded room temperature ductility revealed a marginal gain at large strain owing to the restoration of strain hardening ability. Hardening and softening regimes revealed in a Hall–Petch plot are attributed to the relative evolution of grain boundary characteristics.