Role of high-speed nanoindentation mapping to assess the structure-performance correlation of HVAF-sprayed Cr 3 C 2-25NiCr coating

Cr 3 C 2 -NiCr coatings deposited by high-velocity air-fuel (HVAF) spray can potentially exhibit superior wear performance. However, the microstructural variations caused by altering HVAF process parameters and secondary heat treatment considerably impact coating characteristics and wear performance. The effective characterization of such microstructural variations at the micrometer length scale using conventional techniques is limited. In this study, we employ a high-speed nanoindentation mapping technique to spatially map the properties of HVAF sprayed Cr 3 C 2 -NiCr coating deposited by varying particle size-combustion mode combination, which was in the as-deposited as well as heat-treated state. Despite the significant microstructural heterogeneity at a small scale, the hardness maps show excellent correlation with the microstructure. The data extracted from the nanoindentation maps estimate the area fraction and average hardness of individual phases (carbide, binder, interacted region) in the coatings. Insights on the role of individual constituents on the coating microstructure and mechanical property evolution are presented. The hardness evolution of the individual constituents with processing conditions and secondary heat treatment is correlated with the solid particle erosion performance of the coatings. Overall, Cr 3 C 2 -NiCr coatings deposited through the correct choice of particle size-combustion mode combination and heat treatment improved the desired phase distribution, resulting in superior erosion resistance.