PARAMETER STUDIES ON HIGH-VELOCITY OXY-FUEL SPRAYING OF MCRALY COATINGS

Todays thermally sprayed MCrAlY coatings are commonly manufactured by the vacuum plasma spraying (VPS) process. This technique provides dens e and oxide-free coatings. However, mainly due to the vacuum procedure s this production is cost intensive and time consuming. The third gene ration of high-velocity oxy-fuel (HVOF) systems nowadays offer process ing of materials that are sensitive to oxidation even in atmosphere. T his is mainly due to the achievement of higher kinetic energy of the p articulates and lower melting degrees which enables particle flattenin g in a plastic state. The work presented here focuses the influences o f process parameters of a gas-driven HVOF system on the microstructure and oxygen content of MCrAlY coatings. The major parameters were subj ected to DOE investigation to estimate both single and interacting eff ects. It was found that spray distance, fuel/oxygen ratio and powder f eed rate exert a major influence on microstructure and oxygen content, whereas powder feed gas rate is not significant. Further parameters o f significance are substrate temperature, shroud-gas type, fuel-gas ty pe and powder size fraction. The coatings with the lowest oxygen conte nts were subjected to heat-treatment in vacuum and oxidation in air. S ubsequently they were metallographically investigated. A comparison wi th VPS coatings showed that HVOF-sprayed MCrAlY coatings show similar oxidation behavior. (C) 1998 Elsevier Science S.A. All rights reserved .