Microstructure and mechanical properties of Al2O3–Al composite coatings deposited by plasma spraying

Al2O3 and Al2O3–Al composite coatings were prepared by plasma spraying. Phase composition of powders and as-sprayed coatings was determined by X-ray diffraction (XRD), while optical microscopy (OM) and scanning electron microscopy (SEM) were employed to investigate the morphology of impacted droplets, polished and fractured surface, and the element distribution in terms of wavelength-dispersive spectrometer (WDS). Mechanical properties including microhardness, adhesion and bending strength, fracture toughness and sliding wear rate were evaluated. The results indicated that the addition of Al into Al2O3 was beneficial to decrease the splashing of impinging droplets and to increase the deposition efficiency. The Al2O3–Al composite coating exhibited homogeneously dispersed pores and the co-sprayed Al particles were considered to be distributed in the splat boundary. Compared with Al2O3 coating, the composite coating showed slightly lower hardness, whereas the coexistence of metal Al phase and Al2O3 ceramic phase effectively improved the toughness, strength and wear resistance of coatings.