The hot erosion behavior of HVOF chromium carbide-metal cermet coatings sprayed with different powders

Abstract

The high velocity oxygen fuel (HVOF) sprayed chromium carbide-metal cermet coatings have shown some attractive behavior, which makes them superior to arc-sprayed iron base coatings in preventing erosion. While their hot erosion behavior and its dependence on carbide/metal matrix proportion have been investigated, the detail study of the hot erosion behavior being dependent on the spraying methods and the starting powder characteristics has been somewhat limited. This work was undertaken to understand the influence of powder type on the hot erosion behavior of HVOF coatings. A series of hot erosion tests was carried out on eight chromium carbide-metal cermet coatings using a nozzle type elevated temperature erosion tester. The morphology of specimens was examined by light microscopy and scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS). The composition of starting powders and deposited coatings was analyzed using EDS. It was found that among the eight HVOF chromium carbide-metal cermet coatings tested the composite powder sprayed coatings had nearly the same composition as the starting powders, while the blend powder sprayed coatings had lower chromium and higher nickel contents than the starting powders. This means that more chromium carbide particles had lost during spraying the blend powders, as compared with spraying the composite powders whose composition almost remained the same. The composite powder sprayed coatings also showed higher microhardness and finer microstructure, lower porosity and oxide rate, which account for their higher erosion resistance than the blend powder sprayed coatings.