Effect of graphite nanoplatelets on the mechanical properties of alumina-based composites

Al₂O₃-based composites using exfoliated graphite nanoplatelets (xGnPs) have been developed by powder metallurgy (PM) route using both conventional as well as spark plasma sintering (SPS) processes. Al₂O₃-0.2, 0.5, 0.8, 3 and 5 vol% xGnP composites have been developed, and the effect of the addition of xGnP on the density, hardness, fracture toughness and wear behaviour of the various Al₂O₃-xGnP composites have been analyzed. Conventional sintering was done at a temperature of 1650 °C for 2, 3 and 4 h in inert atmosphere, whereas SPS was carried out at 1450 °C under 50 MPa pressure for 5 min. A uniform dispersion of the xGnP in the Al₂O₃ matrix was observed in the composites upto the addition of 3 vol% xGnP. Results indicate that a significant improvement in hardness, wear resistance and fracture toughness of the composites could be achieved by using xGnP as nanofiller. The hardness and fracture toughness of the composites developed by both conventional sintering and SPS show an increase upto the addition of 3 and 0.8 vol% xGnP respectively. The wear resistance of the composites also shows significant improvement upto the addition of 3 vol% xGnP. The composites developed by SPS have been found to possess superior mechanical properties as compared to the composites developed by conventional sintering. The improvement in the mechanical properties can be attributed to the strong interaction between the xGnP and the Al₂O₃ matrix at the interfaces and to the toughening mechanisms such as crack bridging and crack deflection.