An insight into the properties of ethanol-fueled HVOF-sprayed Stellite-type coatings

The high-velocity oxy-liquid fuel (HVOLF) technique is a promising hypersonic HVOF spraying method designed to enhance coating quality. This study explores the feasibility of using an innovative thermal spray technology, specifically ethanol-fueled HVOF, to fabricate Stellite-type hard-facing coatings. A comprehensive investigation was conducted to examine the correlation between processing parameters —including ethanol-oxygen ratio and stand-off distance (SoD)— and the resulting characteristics and properties of the coatings. The analysis encompassed phase composition, hardness, and microstructural details such as porosity, internal oxidation, deposit efficiency, thickness, and surface roughness. Furthermore, the tribological, corrosion, and oxidation behaviors of the coatings were assessed. The findings indicate that Stellite-type coatings demonstrate adaptability to the processing parameters. The coatings exhibit a relatively dense and uniform structure, with neutral flames followed by fuel-rich gas mixtures, yielding the best microstructural features, i.e., lower porosity and oxide content and enhanced deposit efficiency and thickness. The SoD notably impacts porosity and oxide inclusions for coatings deposited using oxy- and fuel-rich gas mixtures. Analysis revealed that tribo-oxidation with a strain-induced transformation from fcc to hcp structure contributes to reduced wear in denser coatings; on the contrary, this transformation predominantly prevents further sliding wear in coatings exhibiting porosity and oxide content exceeding 3 %.