Microstructural characterizations of Cu processed by ECAP from 4 to 24 passes

The microstructures of pure Cu processed by equal channel angular pressing (ECAP) from 4 to 24 passes were investigated. It was found that the microstructures of Cu samples with a small number of ECAP passes (4-8) were not in homogeneous and the fraction of high-angle grain boundary (HAGB) was low (25 similar to 43%). While for the samples with many number of ECAP passes (12-24), the grains became more equiaxed-like and the GB misorientations exhibited double-peak distribution with high fraction (51 similar to 64%) of HAGB. It was dislocation cells formed in large grains of the few-pass samples, but subgrains in the mail-pass samples. These characterizations suggested that ultrafine-grained (UFG) microstructures in the few-pass samples were not fully accomplished, while it was obtained after many passes (>12). It is believed that dynamic recovery during processing for many passes was attributed to the formation of UFG microstructures.