Oxidation and hot corrosion behavior of multicomponent coatings produced by atmospheric plasma spray

A series of self-lubricating multicomponent coatings (PS series) was developed in the early 1970s to provide low friction and low wear rates while keeping its chemical stability at elevated temperatures. Two compositions of such series, the PS304 (NiCr–Cr₂O₃–Ag–BaF₂/CaF₂) and PS400 (NiMoAl–Cr₂O₃–Ag–BaF₂/CaF₂), are well-established coatings which have shown promising tribological results when tested at a wide range of temperatures. These coatings are candidates to be used on engine parts that may be exposed to corrosive salts at elevated temperature (hot corrosion), but limited data in the open literature are available on the behavior of these coatings under such conditions. Thus, in this study, the hot corrosion and oxidation behavior of PS304 and PS400 coatings were assessed when exposed to a mixture of Na₂SO₄ and MgSO₄ at temperatures ranging from 550 to 950 °C. The coatings were characterized by Raman, scanning electron microscopy, and X-ray diffraction to determine failure mechanisms and corrosion by-products. The PS304 coating has shown to be more prone to oxidation and hot corrosion attack, while PS400 has shown a more stable behavior, even at the highest testing temperature. Based on these results, different mechanisms of oxidation and hot corrosion are proposed for both coatings.