Microstructure and mechanical properties of Al2O3–Cr2O3 composite coatings produced by atmospheric plasma spraying

Al2O3, Al2O3–Cr2O3 and Cr2O3 coatings were deposited by atmospheric plasma spraying. Phase composition of powders and as-sprayed coatings was determined by X-ray diffraction. Electron probe microanalyzer was employed to investigate the polished and fractured surface morphologies of the coatings. Mechanical properties including microhardness, fracture toughness and bending strength were evaluated. The results indicate that the addition of Cr2O3 is conducive to the stabilization of α-Al2O3. Compared with the pure Al2O3 and Cr2O3 coatings, Al2O3–Cr2O3 composite coatings show lower porosities and denser structures. Heterogeneous nucleation of α-Al2O3 occurs over the isostructural Cr2O3 lamellae and partial solid solution of Al2O3 and Cr2O3 might be occurring as well. Furthermore, grain refining and solid solution strengthening facilitate the mechanical property enhancement of Al2O3–Cr2O3 composite coatings.