Sintering behavior of spark plasma sintered alumina with graphene nanoplatelet reinforcement

Graphene nanoplatelet (GNP) reinforced alumina is synthesized by spark plasma sintering (SPS) using process conditions of 1100–1500 °C, 3–10 min dwell time, and 45–90 MPa in order to investigate the effects of GNP on sintering behavior. High volume fractions of GNP (5–15 vol%) are utilized in order to accentuate effects of GNPs. GNP effects on sintering behavior are assessed by evaluating microstructural evolution, grain growth kinetics, and microhardness. The addition of GNPs is found to suppress grain growth by a grain wrapping mechanism resulting in a 10% increase in activation energy when GNP content is increased beyond 5 vol %. Grain growth suppression partially mitigates a decrease in hardness due to the introduction of the soft GNP phase. Evidence of GNPs serving as a sintering aid are seen at short sintering times (3 min), while densification and grain size are observed to level off with extended sintering time (10 min). The application of higher pressures enhances densification, which enables GNPs to more effectively wrap around grains resulting in enhanced grain growth suppression.