The role of microstructural features on the electrical resistivity and mechanical properties of powder metallurgy Al-SiC-Al2O3 nanocomposites

There are many engineering applications in which composite materials are required to satisfy two or more criteria regarding physical and mechanical properties. In this article, Al-matrix nanocomposites reinforced with different volume fractions of SiC nanoparticles (similar to 50 nm; up to 6%) were processed by powder metallurgy (P/M) routes through mechanical milling and hot consolidation techniques. Microstructural studies showed that nanometric Al2O3 particles with a size of similar to 20 nm and volume fraction of similar to 2% were formed and distributed in the metal matrix, owing to the surface oxides breaking. Microstructural analysis also revealed that the size of cellular structure and the density of dislocations increased with the concentration of hard inclusions. However, the limit of deformability of the nanocomposite materials containing a high amount of nanoparticles (> 4 vol%) led to less densification upon hot consolidation stages deteriorating mechanical strength. It was shown that the formation of non-equilibrium grain boundaries with high residual stresses as well as scattering around nanometric inclusions and dislocations influenced the electrical resistivity of the nanocompsites. A linear relationship between the concentration of hard inclusions, electrical resistivity and yield strength was found. This observation demonstrates the importance of substructure and microstructures on the physico-mechanical properties of metal matrix nanocomposites.