The chromia powder can be successfully coated using an air plasma spray system. For spraying, the optimized spray parameters are necessary to obtain the desired mechanical properties. On increasing the arc current, higher values of the CPSP lead to an increase in the partially melted regions while low values of the CPSP lead to high porosity. Moreover,a large SOD leads to early solidification of the molten ceramic droplets before they reach the substrate.
This results in an increase in the porosity of the coating.The mechanical properties such as the hardness, fracture toughness, and Young's modulus largely depend on the coating density. The increase in the porosity reduces the effective hardness and coating toughness. However, the occurrence of the partially melted region results in a slight change in the coating toughness and hardness. The critical load required for crack initiation was determined for all the coatings, and it was observed that this load largely depends on the CPSP rather than the SOD. Finally, the indentation scratch tests performed on the coating specimens revealed that the failure of the plasma sprayed coating that was sprayed at the recommended CPSP, occurred at a higher load. Further, any variation in CPSP or SOD contributed to weak adhesion between chromia coating and the metallic substrate.
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