Prediction of thermo-mechanical behavior and microstructural evolution of copper considering initial grain size at elevated temperature

To characterize and evaluate the workability of pure copper, the hot compression test at temperature range of 673-1073 K, strain rate range of 0.001-0.1s(-1) and two initial grain sizes (IGS) of 20 and 50 mu m with 60% deformation were performed. The results of the true stress-strain curve showed that the processing parameters including IGS, temperature, strain rate, and strain have a significant effect on the elevated temperature behavior of pure copper. As the flow curve of finer grain size at lower temperatures has higher flow stress than the larger grain size which is reversed by increasing the temperature due to changes in the deformations mechanism. A hyperbolic-sine Arrhenius model and strain-compensated Arrhenius constitutive equation with good accuracy were developed to describe and predict the hot flow behavior of this material. The activation energy was determined in different processing conditions for two different IGS and the results showed that this energy increases with increasing strain, and its values are greater for finer grain sizes. The investigation of the deformation mechanism showed that the mechanism of cross-slip and dislocation climb controlled the deformation process are dominant mechanisms for IGS of 20 mu m whereas self-diffusion is the dominant mechanism for IGS of 50 mu m. To determine the safe and optimal conditions for hot deformation, the processing maps were drawn based on DMM theory at different strains. Finally, by examining and evaluating the microstructure under different processing conditions, the dominant mechanisms were identified for the two investigated IGS at different temperature ranges and strain rates, and the safe and unsafe domains were specified for the hot deformation of copper.