Strengthening and deformation mechanisms of oxygen-modified nanocrystalline Cu

Despite the crucial role of oxygen in metallic materials, its effect on strengthening and deformation at the atomic scale remains poorly understood. We investigated the influence of oxygen on the microstructure and strengthening of commercial pure copper processed by high-pressure torsion. Advanced transmission electron microscopy (TEM) studies, combined with atomic-scale quantitative analysis and theoretical calculations using density functional theory (DFT), reveal that the introduction of oxygen intensifies lattice distortion and impacts crystal deformation behavior. Comprehensive research discovered that, contrary to our previous understanding, oxygen can actually suppress grain refinement before the microstructure reaches a steady state (or saturation). At this stage, oxygen exists in multiple forms, including oxides (CuO, Cu₂O), interstitial solutes, and oxygen-rich clusters. Furthermore, the synergy of strengthening mechanisms, including oxide dispersion, solid-solution strengthening, grain boundary pinning, and coherent interface strengthening, results in a significantly improved hardness compared to pure copper Cu nanocrystals. This study provides a new insight into the role of oxygen in nanocrystalline materials. It also demonstrates that oxygen incorporation during severe plastic deformation is an effective and cost-effective strategy for tailoring the microstructure and enhancing mechanical properties.