The deformation of single crystals of copper and copper-zinc alloys containing alumina particles - II. Microstructure and dislocation-particle interactions

Abstract

Electron microscope studies of deformed single crystals of Cu and Cu + Zn alloys of various compositions containing small alumina particles show that the dislocation structures generated and associated with the particles consist generally of prismatic loops, Orowan loops as well as prismatic loops in some brass alloys, and groups of dipoles. The formation of predominantly interstitial prismatic loops is explained in terms of a cross-slip mechanism controlled by the interstitial misfit strains around the particles. The transition from prismatic loop to prismatic plus Orowan loop structures in the brass alloys for Zn contents greater than ca . 20 wt % is considered to be due to the dependence of the activation energy for cross-slip on the stacking fault energy and to the solution hardening friction stress. In the Cu + 20% Zn alloys, measurements of the height of the loops and their numbers show that some dislocations by-pass the particles without forming loops. The mechanism of cross-slip leading to the formation of prismatic loops or ‘by-passing’ is discussed in some detail. The number of prismatic loops generated decreases with temperature. This fact is explained in terms of pipe or interface diffusion controlled climb of dislocations at the particles.