Microstructure and wear properties of atmospheric plasma-sprayed Cr3C2-NiCr composite coatings

Gas turbines and other critical power generation components in coastal areas are susceptible to corrosion and erosion due to solid particle erosion by air-borne particles, humidity, and sea salt, that severely damage the parts. The synergistic effect of both erosion and corrosion can accelerate the material degradation process compared to the individual effects, which might thus lead to less safety, economic loss, and in extreme cases, rapid failure of the components. Cr3C2-NiCr coatings around 150 to 250 mu m are commonly used to safeguard these high-valued components. To further enhance the wear resistance of the base coating's secondary particles, B4C and Cr2O3 were added (5 and 10% weight fraction). These coatings were deposited on SS 304-L substrate material by using the atmospheric plasma spray process and Metco TriPlex Pro-210 gun. The microstructure, microhardness, contact stiffness, fracture toughness, sliding wear and dry erosion resistance of the as-deposited coatings were investigated. The results showed that there was a slight phase change Cr3C2-NiCr composite powder after the spraying process. The developed coating has a dense microstructure with relatively low defects such as micro-cracks and pore; high hardness, and toughness. Among all the tested coatings, Cr3C2-NiCr coating, with a 10% weight fraction of Cr2O3 exhibited high wear resistance under all conditions. Cr3C2-NiCr with 10% Cr2O3 exhibited an almost 3.12 times lower wear rate and almost 1.15 times higher erosion resistance than the base coating (Cr3C2-NiCr). This improvement in the wear resistance could be attributed to the improvement in hardness and fracture toughness of the coating material after the addition of hard secondary phases. Morphology of wear samples was analyzed using SEM to investigate the damage mechanism.