The influence of HVOF powder feedstock characteristics on the abrasive wear behaviour of Cr xC y–NiCr coatings

Abstract

Cr x C y –NiCr cermet coatings are commonly utilised in industry as a means to provide wear resistance in high temperature environments. Such coatings are usually deposited by thermal spraying. In this work, Cr x C y –NiCr coatings have been deposited using a Miller Thermal/UTP Top Gun high velocity oxy-fuel spray system from three commercially available powders, namely a sintered and crushed powder, a blended powder and a composite powder. The characteristics of the powder feedstock have a strong influence on the coating microstructures, although the coating microstructure is often very different to that of the powder due to processes that occur during spraying and rapid solidification of the splats. Coating microstructures were assessed by X-ray diffraction, scanning electron microscopy and microhardness measurements. The abrasive wear performance of the coatings was assessed using a dry sand–rubber wheel test with both alumina and silica abradents. It was found that, under all conditions, the coating deposited from the blended powder exhibited the highest wear rates and the coating deposited from the composite powder exhibited the lowest wear rates. Wear mechanisms were assessed by SEM examination of the wear surfaces and cross-sections through the wear scars and understood in terms of the different coating microstructures.