Wear and microstructure analysis of Cr-Ni multilayer functionally graded coatings on SS304 by high velocity oxygen fuel (HVOF) spraying

Components operating in extreme conditions within the power generation, marine, and aerospace industries often experience severe surface degradation due to erosion, wear, and corrosion caused by solid particles, silt, cavitation, and slurry. This study compares the tribological performance of two multilayer coatings, Coating A and Coating B, both comprising five graded layers transitioning from Cr to Ni. The coatings were deposited using high velocity oxygen fuel (HVOF) spraying, with ball-milled Ni and Cr powders as feedstock materials. Comprehensive characterization of the coating’s microstructure, crystallographic, and wear analysis was conducted using scanning electron microscopy (SEM), Electron Backscatter Diffraction (EBSD), and Pin on Disc. Despite identical compositional structures, differences in wear and friction behavior were observed due to variations in microstructure and interfacial bonding. Coefficient of friction (COF) and wear rates were evaluated under normal loads of 20 N, 30 N, and 40 N. Coating A exhibited higher and more fluctuating COF values, reaching up to 0.293 at 40 N, while Coating B maintained lower and more stable COF values, peaking at only 0.249. Wear analysis revealed significantly higher wear for Coating A (161.04 µm at 40 N) compared to Coating B (132.59 µm at 40 N). Friction force measurements further confirmed the superior performance of Coating B, which showed lower and more consistent values—stabilizing between 11.5 and 12.5 N at 40 N—versus 14.5–15.5 N for Coating A. SEM analysis of worn surfaces revealed severe abrasive and adhesive wear with accumulated debris in Coating A, especially under high loads. In contrast, Coating B showed evidence of controlled wear, including spalling and protective oxide layers, even at elevated loads. Overall, Coating B demonstrated superior tribological behavior due to improved microstructural integrity, layer cohesion, and wear resistance.