Abstract

The cavitation erosion of various hardfacing coatings was investigated by using a vibratory cavitation apparatus according to ASTM G 32. Coatings of austenitic stainless steel containing 10 % cobalt were applied by arc welding. High velocity oxy-fuel spraying (HVOF) was employed to produce coatings of various kinds of cermets and metallic alloys. For each coating, the steady state erosion rate was determined and the effect of process parameters and alloy composition on the microstructure and erosion rate was investigated. The morphology and microstructure of the coatings before and after cavitation testing were analysed by metallographic methods in order to study the erosion mechanism. It is demonstrated that the high resistance to cavitation erosion of the cobalt-alloyed steel can even further increase when the fluxed core arc welding process and an improved pulsed power source are used to produce the coatings. The erosion resistance of the HVOF coatings, however, was limited by pores, microcracks and oxides and did not significantly exceed the level typical for bulk stainless steel 316 L.

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