Isothermal oxidation and hot corrosion behavior of HVOF sprayed 80Ni-20Cr coatings at 750 °C

Abstract

NiCr thermal spray coatings are widely used in many different industrial areas, especially in aviation, automotive, and thermal power plants, in order to obtain abrasion resistance. The determination of high-temperature properties is of great importance in terms of determining the limits to which the coating can operate without being damaged and its structural stability. In this study, 80Ni-20Cr alloy powder was deposited onto 316L stainless steel substrates using a high velocity oxygen fuel (HVOF) spraying technique, and the coatings' oxidation and corrosion behaviors at high temperatures were assessed. In this context, while isothermal oxidation tests were conducted at 750 °C for 5, 25, 50 and 75 h, the hot corrosion behavior of the coatings was investigated for 1, 3 and 5 h at 750 °C in an environment consisting of a 55 wt% V2O5–45 wt% Na2SO4 corrosive salt mixture. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were used to evaluate powder feedstock and as-deposited, oxidized, and corroded coating samples' phase formation and microstructural changes. In all cases, the coated samples showed good resistance to isothermal oxidation, with no damage such as flaking and peeling. No oxide formation was observed on the coating surfaces. The oxidation started from the coating and substrate interface and proceeded towards the coating surface. Following the hot corrosion experiments, it was observed that the 80Ni-20Cr coating's reaction with the vanadate-sodium sulfate melt resulted in the formation of the corrosion product Ni3V2O8 in all time periods. As a result, under high temperature oxidation and hot corrosion environmental conditions, 80Ni-20Cr coatings have been observed to retain their durability without major damage.