Gradient microstructure,recrystallization and mechanical properties of copper processed by high pressure surface rolling

The microstructure,hardness and tensile properties have been studied in copper processed by high pressure surface rolling(HPSR)both in the as-deformed condition and after subsequent annealing at 150℃.It is found that a gradient structure with significant differences in the scale of microstructural features is formed by HPSR.The deformed microstructure varies from nano-and ultrafine-scale structures with a large fraction of high angle boundaries near the surface to lightly deformed grains at depths of 1-3 mm below the surface.Tensile tests of 1-mm-thick specimens demonstrate that the asdeformed material has a high strength and a low uniform elongation.Annealing at 150℃results in partial recrystallization,which creates new through-thickness gradients.Except for the topmost layer and several bands in the adjacent layer,recrystallization is more pronounced close to the surface.The fraction recrystallized is at least 80%at depths of 60-300μm after annealing for 960 min.The fraction recrystallized in the subsurface decreases with increasing depth,and the deformed layer at depths greater than 500μm re-mains largely non-recrystallized after annealing.This partially recrystallized condition demonstrates an improved combination of strength and ductility.

Evolution of microstructure and texture in copper during repetitive extrusion-upsetting and subsequent annealing

The evolution of the microstructure and texture in copper has been studied during repetitive extrusionupsetting（REU） to a total von Mises strain of 4.7 and during subsequent annealing at different temperatures. It is found that the texture is significantly altered by each deformation pass. A duplex 001 ＋ 111 fiber texture with an increased 111 component is observed after each extrusion pass,whereas the 110 fiber component dominates the texture after each upsetting pass. During REU, the microstructure is refined by deformation-induced boundaries. The average cell size after a total strain of 4.7 is measured to be ~0.3 μm. This refined microstructure is unstable at room temperature as is evident from the presence of a small number of recrystallized grains in the deformed matrix. Pronounced recrystallization took place during annealing at 200？C for 1 h with recrystallized grains developing predominantly in high misorientation regions. At 350？C the microstructure is fully recrystallized with an average grain size of only 2.3 μm and a very weak crystallographic texture. This REU-processed and subsequently annealed material is considered to be potentially suitable for using as a material for sputtering targets.