Synergistic strengthening mechanisms of copper matrix composites with TiO2 nanoparticles

The trade-off between strength and ductility has been a dilemma in copper matrix composites. In this work, we introduce a way of strengthening copper matrix composites containing TiO2 nanoparticles with remarkable ductility. The Cu-8wt%TiO2 composites were fabricated using the powder metallurgy route with spark plasma sintering (SPS) for different holding times incorporating hot extrusion. The sintered composites for longer holding times showed an inhomogeneous distribution of large dispersed particles located mostly along the grain boundaries. However, tensile strength was improved compared with pure copper while ductility was reduced. In contrast, after hot extrusion, a homogeneous distribution of reinforcement particles and grain refinement concurrently triggered strong strengthening and enhanced ductility. The contribution of synergistic strengthening mechanisms, i.e. Hall-Petch strengthening, Orowan pinning, dislocation density and load transfer effect, was studied and the key strengthening mechanisms were elucidated. It was found that composite yielding was strongly affected by sintering time, particulate size and interparticle spacing so that HExt-SPS@30min composite presented the excellent yield strength of 290 MPa, about 72% above pure copper.