Phase evolution and microstructure of suspension HVOF-sprayed alumina coatings

Abstract

High-velocity oxygen fuel (HVOF) spraying enables the deposition of particulate ceramic materials, producing dense coatings in the micrometer to millimeter range that are particularly suitable for coating metallic parts for demanding environments. Alumina (Al₂O₃) is one of the most commonly used feedstocks for thermal spray coatings because it has good dielectric properties, excellent hardness, and corrosion resistance while being cost-effective. In this work, alumina coatings from two aqueous suspensions with different particle size distributions were processed by HVOF spraying. Rietveld refinements of the X-ray diffraction (XRD) data were used to quantitatively determine the phase content within the as-sprayed coatings. The phase composition was further explored using the electron backscatter diffraction (EBSD) method. Our work provides strong evidence for the higher retention of the thermodynamically stable α-${\mathrm{Al}}_2{O}_3$ phase in suspension HVOF-sprayed coatings compared to the powder counterpart. In addition, the impact of key processing parameters was studied, providing guidance for the production of particular phase compositions and microstructures tailored to specific application requirements.