Microstructure and properties of nano-C and in-situ Al2O3 reinforced aluminum matrix composites processed by high-pressure torsion

In this study, Al-Si matrix composites reinforced with In situ Al2O3, C nanotubes (CNTs), and graphene nanoplatelets (GNPs) were prepared by ball milling, hot-isostatic pressing (HIP), and subsequent high-pressure torsion (HPT). Microstructures, interfacial bonding, and electrical and mechanical properties of the composites were analysed. In situ Al2O3 particles and whiskers were formed via reaction between Al powder and SiO2 powder. Grains of the composites were significantly refined and reinforcements were well dispersed in the matrix by HPT. A sub-micron equiaxed grain structure with an average grain size of 0.60 mu m was obtained. Interface between the CNTs and the matrix was narrow and had no brittle phase. With an increase in the number of HPT cycles, microhardness and electrical conductivity of the composites increased. Strengthening mechanism of the Al matrix composites was mainly fine-grain strengthening. Dislocation accumulation and grain boundary evolution caused by HPT were examined.