Study of the elastic properties and thermal shock behavior of Al–SiC-graphite hybrid composites fabricated by spark plasma sintering

Abstract Al–SiC and hybrid Al–SiC-graphite MMCs with up to 70 vol% SiC and 10 vol.% graphite were fabricated using spark plasma sintering. Detailed studies of the microstructure, Vickers hardness, longitudinal elastic constant C11, as well as thermal shock resistance of the MMC samples were carried out. Non-destructive ultrasound phase spectroscopy was used to measure the C11 elastic constant of the MMCs, and the measured values were compared with different micromechanical models for particle reinforced composites. For both two- and three-component MMCs, the Hashin Shtrikman lower bound fitted best to the experimental results in the absence of any porosity. Thermal shock resistance of the MMCs was carried out by heating in air to 500 °C and subsequently quenching in water for ten times. The extent of thermal shock-induced structural alteration was determined via a systematic study of the change in density, hardness, and C11 of the samples. It is observed that the thermal shock resistance of the MMCs depends upon multiple factors such as SiC content, graphite content, and the amount of residual porosity. While the reduction in mechanical properties of the Al–SiC MMCs due to graphite addition is according to the expected line, the present study shows that graphite addition also reduces the thermal shock resistance of the MMC.