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Selection and characterisation of HVOF cermet coatings for volutes of high capacity pumps of opencast lignite mines

The centrifugal pumps made of grey cast iron deployed in mining conditions encounter severe erosion and corrosion problems causing sudden failures. To combat this, the thermal spray ‘high velocity oxyfuel’ (HVOF) process was selected to provide a cermet coating, namely, WC–Co–Cr–Ni. After design investigation on coatings, erosion and corrosion experiments were conducted and characterisation studies involving microstructure, surface morphology and energy dispersive X-ray fluorescence analysis were made. The operating parameters on the different sections of impact volute surface were assessed and accordingly, the coating thickness was designed scientifically for maximum impact loads and minimum corrosion failures. The life of the coated pump casings has been improved up to 12 times by optimising the coating thickness.