Efficacy of graphene nanoplatelets on splat morphology and microstructure of plasma sprayed alumina coatings

Splat morphology and its microstructure are of significance to affect the comprehensive properties of plasma sprayed ceramic coatings. This paper studies the effect of graphene nanoplatelets (GNPs) on the splat morphology and microstructure evolution of plasma sprayed alumina coatings. With an increasing GNP content, splat morphology became more disk-shaped and the average diameter of the splat decreased from 120 +/- 28 mu m for pure Al2O3 to 83 +/- 17 mu m for 1.0 wt% GNP/Al2O3. Simulated splat morphology presented a good agreement with the experimental observations. GNP agglomeration at the periphery of a droplet accelerate the formation of solid ring resulting in a decrease in splat diameter, and homogeneously distributed GNPs inside a droplet is expected to simultaneously promote rapid solidification of inward melt following the formation of a solid ring, which suppresses splat fragment. Meanwhile, columnar grain refinement and GNP pull-out are responsible for the composite splats free of microcracks.