Erosion Wear Characteristics of Surface Modified Grey Cast Iron by WC-Co-Cr/NiCrBSi Coating Using HVOF Thermal Spray Process

Pump casings made of grey cast iron (GCI) used in lignite mines for dewatering are subjected to erosive wear and fail catastrophically. An attempt was made to modify the surface of GCI by WC-Co-Cr/NiCrBSi coating using HVOF process for the application under mining conditions. Grey cast iron samples with and without WC-Co-Cr/NiCrBSi coating were subjected to slurry jet erosion tests by varying the impingent velocity and angle under two different pH conditions of 3 and 7 which pertain to the mining environment. XRD characterization was done to identify and confirm phase composition. Eroded surface morphology studies were carried by SEM on both the substrate and coating, which revealed the erosion of GCI surface, predominantly due to ploughing mechanism. In the case of WC-Co-Cr and NiCrBSi coating, at an oblique angle of impact, the material removal from the surface is by micro cutting of the matrix, ploughing, and abrasive mode mechanisms. At normal impingement, the fluctuating stress creates the cracks, which interlink each other to form lips and craters followed by material degradation through fatigue. Performance of WC-Co-Cr coating is found to be better than NiCrBSi Coating.