Understanding structural evolution of nanostructured Cu-Al2O3 composite powders during thermomechanical processing

Abstract

A better understanding of structural coarsening mechanisms is of significance to effectively tackle structural instabilities in nanostructured materials. In this work, the microstructural evolution of nanostructured metallic powder particles during thermomechanical consolidation has been investigated to gain new insights into the evolution of reinforcing particles and matrix grains of a mechanically alloyed nanostructured Cu-5 vol.% Al2O3 composite powder extruded at either 300 or 900 °C, respectively. Unusual coarsening of Al2O3 particles and rapid growth of Cu grains occurred during extrusion at a low temperature of 300 °C; meanwhile the formation of elongated micron Cu grains was observed at a high extrusion temperature of 900 °C. Both the applied shear stress/strain and the sizes and distribution of second-phase nanoparticles were found to determine the grain structure of the Cu matrix after extrusion. Specifically, the shear stress-induced dynamic and particle-stimulated recrystallization and the movement of the Al2O3 particles are respectively responsible for the low-temperature rapid growth of the Cu grains and the coarsening of the Al2O3 particles. The development of the elongated micron Cu grains during extrusion at 900 °C is associated with anisotropic grain boundary migration and particle re-distribution.