Structural changes of the Cu-0.6Cr alloy upon cooling at different rates after a large high-temperature deformation

Abstract

The present work studies changes in the structure of samples of the Cu-0.6Cr alloy in the state of a supersaturated solid solution, subjected to large plastic deformation by upsetting by 90% (e ≈ 2.0) at a temperature of 800°С and cooling in various environments: liquid nitrogen, water and air, providing different cooling rates of the material. It is shown that the cooling rate has a decisive influence on the type of structure formed. It was found that in the Cu-0.6Cr alloy, a decrease in the cooling rate leads to a decrease in the fraction of high-angle boundaries and to the formation of a finer structure at the meso and micro levels. At the same time, strength and conductivity values grow. At a high cooling rate (liquid nitrogen), the structural state corresponding to the stage of dynamic recrystallization and polygonization is observed. Such a structure has a low dislocation density and more perfect boundaries. When cooling in air at the first stage, post-dynamic recrystallization processes develop, associated with the nucleation of new nuclei of recrystallized grains along the boundaries of deformed grains, as well as the development of a substructure. The average grain and subgrain size decreases to 1.7± 0.2 and 1.1± 0.2 μm, respectively. With further cooling, from a temperature of ≈600°С, two competing processes that develop during aging obviously begin to occur, namely, the recovery of the structure and the decomposition of the solid solution. This is evidenced from a decrease in the lattice parameter and an increase in electrical conductivity (up to 79% IACS), and the close interaction of dispersed particles 5-10 nm in size and dislocations leads to the further development of the substructure. At the same time, the proportion of middle-angle boundaries increases and the proportion of twin boundaries decreases, while the proportion of high-angle boundaries of the general type remains practically unchanged.