Effect of the MgO particles on the nanocrystalline copper grain stability

Abstract

The study is centred on the microstructure evolution in Cu–3 vol.% of MgO composite during the preparation of a nanocrystalline powder and its processing into a macroscopic compact and thermal loading. The effect of dispersed oxide phase on the preservation of the initial nanostructure is analysed. Due to the weak coherency of the Cu/MgO interface, the Cu matrix is not sufficiently controlled by the MgO during heating. Some portions of the oxide nanoparticles agglomerate into coarser particles (>50 nm), which are less efficient barrier against the grain growth. Fine particles retard the grain growth. The consolidation results in a bimodal grain size distribution with micrometre-sized grains embedded inside a matrix of nanocrystalline/ultrafine grains. The fine, dispersion-strengthened grains provide good strength, as expected from an extrapolation of the Hall–Petch relationship. The inhomogeneous microstructure induces strain-hardening mechanisms that stabilize tensile deformation, leading to high tensile ductility.