Effect of processing route on grain refinement in pure copper processed by equal channel angular extrusion

An experimental study of the microstructures in pure copper billets processed by 8 passes of equal channel angular extrusion (ECAE) via an extended range of processing routes with a 90 degrees die is carried out. Each processing route is defined according to the inter-pass billet rotation angle (chi), which varies from 0 degrees to 180 degrees. According to the generation of high-angle boundaries and reduction of grain size by electron backscatter diffraction (EBSD) measurements, the grain refinement is found to be most efficient for route with chi=90 degrees and least efficient with chi=180 degrees, among the seven routes studied. This trend is supported by supplementary transmission electron microscopy (TEM) measurements. Comparison of the EBSD and TEM data reveals the importance of considering the non-equiaxity of grain structures in quantitative assessment of microstructural differences in ECAE-processed materials.