Strain softening in oxygen free high conductivity (OFHC) copper subjected to repetitive upsetting-extrusion (RUE) process

Oxygen Free High Conductivity (OFHC) copper was subjected to severe plastic deformation using Repetitive Upsetting-Extrusion (RUE) process at room temperature. Numerical simulation up to 10 cycles of RUE was carried out to estimate the strain distribution across the cross-section of the RUE processed samples. The strain obtained from the finite element analysis (FEA) was correlated with the microstructure and microhardness obtained by carrying out RUE experiments up to 10 cycles. The microhardness of the material initially increases sharply with strain, reaches a peak and thereafter decreases rapidly to finally attain a steady state. The decrease in hardness after a peak is attributed to the decrease in the output of Frank-Reed sources as discussed in the modified ETMB or Kinetic model.