Microstructural and textural characterization of copper processed by ECAE

A submicron grain (SMG) microstructure, with an average grain size of about 0.4 μm was produced by equal channel angular extrusion (ECAE). Samples were examined at various scales using the transmission electron microscope (TEM), the scanning electron microscope (SEM) and the field emission gun (FEG/SEM) with electron-backscattered diffraction (EBSD) and also the neutron diffraction. After 8 passes into the channel, which corresponds to a total strain of about 8, the SMG microstructure was composed of large dynamic recrystallized grains within a poorly recovered matrix. A quantitative study of microstructural parameters, such as average low and high boundary spacings, grain and subgrain aspect ratios and crystallographic orientations, shows in particular that the area fraction of low angle boundaries is still very high (60%) and as a consequence the microstructure is not a true submicron grain structure required to resist recrystallization during annealing. Indeed, annealing at 200 °C in oil leads to a stable but not submicron structure, with a grain size of about 2 μm.