Microstructure and mechanical properties of plasma sprayed alumina-based coatings

Alumina-based coatings are employed in many industrial applications, in order to protect the surface of metal components against high temperature, wear, corrosion and erosion. In this work two different alumina-based coatings were fabricated by atmospheric plasma spraying (APS), starting from powder particles composed of pure Al2O3 and Al2O3-3 wt% TiO2, respectively. Their phase composition was investigated by X-Ray Diffraction (XRD) and revealed that both the as-sprayed coatings were mainly composed of metastable γ- and α-Al2O3 phases. The γ phase recrystallized to α phase after heat treatment. The porous microstructure was analyzed by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). Thin TiO2-rich splats were observed within the microstructure of alumina-titania coatings. The pure alumina coatings exhibited similar porosity and higher microhardness than the alumina-titania ones (12.8 against 9.9 GPa). Both the coatings herein analyzed are particularly promising for high-temperature anti-wear applications, because of their enhanced mechanical properties.