Sliding wear behaviour of WC-Co reinforced NiCrFeSiB HVOAF thermal spray coatings against WC-Co and Al2O3 counterbodies

Abstract NiCrFeSiB alloys reinforced with WC-Co are potentially useful composite coating materials for use in applications in which resistance to sliding wear, hot corrosion and high temperature is required. Furthermore these materials offer an advantage over WC-Co and WC-CoCr coatings in applications where a more ductile coating is required. A powder feedstock containing a 50/50 mixture of WC-Co/NiCrFeSiB was sprayed by HVOAF (high velocity oxy-air fuel) thermal spray torch, which was developed by Monitor Coatings Castolin Eutectic for internal diameter applications, with two sets of spray parameters with the overall gas flowrate entering the torch changed. The powder feedstock and sprayed coatings were characterised using SEM imaging, XRD and measurement of mechanical properties such as microhardness and indentation fracture toughness. The specific wear rates of the coatings were measured when testing the coatings against WC-Co and Al2O3 counterbodies and it was determined that the coating sprayed at the higher gas flowrate wore out less against both counterbody materials, due to its superior microhardness. Tests against the Al2O3 counterbody lead to increased material loss of both coatings in comparison to testing against WC-Co. This was due to the wear of the Al2O3 ball throughout the test leading to an increase in contact area between the coating and counterbody.