Nano-grain refinement and strengthening of copper under room temperature RUE process

Abstract

In this investigation, the Repetitive Upsetting-Extrusion (RUE) process was used to investigate effect of severe plastic deformation on the microstructural changes and flow behavior of commercial pure copper. Initial materials together with two, four, and eight passes of RUE under annealing and non-annealing conditions were studied. Results show that grain refinement, on the scale of nanometer, has been mostly achieved only after two passes of RUE, which is essentially a combination of one upsetting and one extrusion path. Increasing the number of passes, following four RUE passes, did not have discernible effect on the grain refinement. Such behavior is explained through saturation of dislocations and the formation of high angle grain boundaries after only two passes of RUE. The grains even became slightly larger after eight passes of RUE process as compared to the two and four passes of RUE; such a result corresponds to restoration phenomena occurring during a high number of passes of RUE process. Flow strength of the material after different passes substantially increased, though the rate at which the flow stress increased declined by increasing the number of passes. ETMB model was used to explain the deformation behavior of the RUE samples.