Studies on high temperature erosion behavior of HVOF-sprayed (Cr₃C₂-NiCr)Si and WC-Co/NiCrAlY composite coatings

The present study investigates the high temperature erosion behavior of HVOF sprayed composite coatings on T11 steel substrates by studying (Cr₃C₂-NiCr)Si and WC-Co/NiCrAlY coatings. Phase composition, cross sectional microstructure, mechanical properties, and erosion resistance were analyzed by XRD, EDS, SEM and three-dimensional optical profilography. The results demonstrate that the WC-Co/NiCrAlY coating has higher erosion resistance and oxidation stability for all temperatures and impact angles tested. Its enhanced performance in high temperature and erosive conditions is attributable to the formation of stable protective oxides such as Al₂O₃ and Cr₂O₃ and intermetallic phases such as Ni₃Al and Cr₃C₂. The NiCrAlY matrix prevents significant decarburization of WC particles, and hence phase stability and oxidation resistance. The (Cr₃C₂-NiCr)Si coating has higher microhardness due to silicide phases, but is more vulnerable to direct impacts and inferior oxidation resistance. The phase transformations for both coatings are favorable at elevated temperatures which enhances erosion resistance. The WC-Co/NiCrAlY coating is smooth and shallower in erosion craters and is perfectly suited for harsh environments demanding high toughness, impact resistance and oxidation stability. For applications in which high hardness is needed in less severe conditions, the (Cr₃C₂-NiCr)Si coating is more suitable.