The Effect of Spray Distance on the Hot Corrosion Behavior of HVOF-Sprayed NiCrAlY Coatings in a Simulated Gas Turbine Environment

To utilize the unique properties of coatings produced using the high-velocity oxy-fuel (HVOF) method, this study examined the effect of spray distance on the hot corrosion behavior of NiCrAlY coatings deposited on a steel substrate. The coating samples were obtained at spray distances of 20, 25, and 30 cm. The flow rates of oxygen and propane were maintained constant at 300 and 60 lit/min, respectively. Additionally, the powder feeding rate was 32 g/min. The samples were then subjected to the hot corrosion test in a salt mixture of Na₂SO₄−60% V₂O₅ at 900°C in an ambient atmosphere. The surface and the cross section of the samples were observed using a scanning electron microscope (SEM) and the chemical composition of different sections was determined by energy-dispersive spectroscopy (EDS). The phases were also characterized using X-ray diffraction analysis (XRD). The best corrosion resistance was found in the sample coating formed at a spraying distance of 20 cm, as the results showed that increasing the spraying distance led to a reduction in the thermal and kinetic energy of the flame, resulting in increased porosity in the coating. This behavior can be attributed to the low oxide content of the coating, the higher aluminum content, and the richer NiAl phase, which serves as a reservoir for aluminum.