Dissolution of the second phase particles in the course of the equal channel angular pressing of diluted Cu-Cr-Zr alloy

Abstract

Changes of properties and the second phase particles' distribution in diluted CuCrZr alloy in the course of equal channel angular pressing (ECAP) and post-deformation annealing are investigated. To decrease the concentration of alloying elements dissolved in the copper matrix, samples of the alloy were thermally aged prior to the ECAP. Temperature of annealing, 450 degrees C, was the same as the one used for the subsequent post-deformation aging, and the time of annealing was long enough to reach a practically equilibrium state. The enthalpy release rate curve of the ECAP-processed sample, unlike the one for the initial state exhibits an exopeak in the temperature range 440..470 degrees C, which is typical for breakdown of the solid solution in alloys of this system. The post-deformation aging causes a significant increase in the tensile strength as compared to the value immediately after the ECAP. This increase can be related only to the dispersion strengthening that is confirmed by the observation of higher density of particles after the aging. These facts unambiguously indicate that the solid solution at the aging temperature is supersaturated, i.e. its concentration increased in the course of the ECAP due to the deformation-induced dissolution of the second phases. This conclusion agrees with the behavior of the electrical conductivity that noticeably decreases upon the ECAP and recovers its initial value after the aging. As the density of structural defects is significantly different in the initial and final states, the observed decrease can be related only to the lattice distortion due to dissolved foreign atoms.