Cavitation Erosion Resistant Coatings Produced by Thermal Spraying and by Weld Cladding

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.

Properties of WC‐CoCr Based Coatings Deposited by Different HVOF Thermal Spray Processes

“…The reasons for greater decomposition of the powder during spraying with the gas‐fuelled HVOF system are that the powder is injected directly into the combustion chamber, whereas in the liquid‐fuelled gun the particles are injected into nozzle downstream of combustion. Moreover, systems which employ a gaseous fuel such as hydrogen yield comparatively higher particle temperatures and lower velocities than systems which employ a liquid fuel such as kerosene 11, 13. As consequence, a higher temperature combined with a lower velocity increases the residence times of the particles in the hot gas.…”

Optimization of Testing Method in Comparison with the Coated Composites and Metals by Vibratory Cavitation Test

“…[12] Cavitation rates obtained from this modified testing procedure usually show 40-60% of the rates determined with the standardized procedure according to ASTM G32. [11] Fig. 4 shows the comparison between standard test and modified test with decreasing total weight loss in distilled water and sea-water.…”

“…The cavitation-erosion experiments had carried out by a form of round robin [10] that recommended ASTM [11] using a vibratory apparatus according to ASTM G32. The standardized test and modified test basically consists of ASTM G32 condition that pulsates in fluid (distilled water and sea water) bath at a frequency of 20kHz and a amplitude of 50 .…”