Nanostructured zirconia-30 vol.% alumina composite coatings deposited by atmospheric plasma spraying

Nanostructured zirconia-30 vol.% alumina composite coatings were deposited by atmospheric plasma spraying using nanosized ZrO2 and Al2O3 powders. The microstructure and phase composition of the coatings were characterized by electron probe X-ray microanalyser (EPMA), field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and Raman spectroscopy. Microhardness (HV0.2kg) and roughness (Ra) were also measured. The as-sprayed coating exhibited a bimodal structure: the typical lamellar structure comprised of nanosized columnar grains and the nanosized equiaxed grains. Alumina-rich splats were dark grey colored and non-uniformly embedded in light grey zirconia-rich splats. No monoclinic or cubic zirconia phase and alumina phase were detected in the as-sprayed coating. Compared to pure zirconia coating, the microhardness of the as-sprayed coating increased from 5.7 GPa to 8.4 GPa, and the roughness increased from 3.74 μm to 6.03 μm with the addition of alumina into feedstock.