Improved properties of Al-Si3N4 nanocomposites fabricated through a microwave sintering and hot extrusion process

Abstract

In this study, nano-sized Si3N4 (0, 0.5, 1.0 and 1.5 vol%)/Al composites were fabricated using a powder metallurgy method involving microwave sintering technique followed by hot extrusion. The influence of Si3N4 content on the structural, mechanical and thermal behaviour of Al–Si3N4 nanocomposites was systematically investigated. Electron microscopy examination reveals the uniform distribution of hard Si3N4 nanoparticles in the soft Al matrix. The compressive and tensile strengths of Al composites increased with the increase of Si3N4 content while the ductility decreased. The thermal expansion coefficient of the Al composite decreased with the progressive addition of hard Si3N4 nanoparticles. Overall, hot extruded Al–1.5 vol% Si3N4 nanocomposites exhibited the best combination of tensile, compressive, hardness, Young's modulus and thermal properties of 191 ± 4 MPa, 412 ± 3 MPa, 16.3 ± 0.8 GPa, 94 ± 2 GPa and 19.3 μ K−1, respectively. Tensile tests performed at 200 °C revealed that the tensile strength reduced by ∼35% when compared to the strength at room temperature. The strength, however, was still higher compared to that of the pure Al at 200 °C. The major enhancement in the strength of the nanocomposites is primarily attributed to the presence of uniformly distributed nano-sized Si3N4 nanoparticles in the Al matrix.