Abstract
Alumina–zirconia nanostructured coatings were formed on 7075 Al alloy through Plasma Electrolytic Oxidation (PEO) operated in aDC potentiostatic mode. The composite coatings were produced in the range of 425–500V in an alkaline electrolyte containing 4g/LK2ZrF6. Tribological properties of coatings were investigated using dry sliding wear test against WC balls with a pin-on-disc tribometer. Wear rates were evaluated using optical profilometer. It was shown that the nanostructured alumina–zirconia composite coatings can be formed at voltages ≥450V. The coating thickness and roughness were in the range of 15.2–24.2μm and 0.68–2.35μm, respectively. The distribution of Al, Zr and O in the coatings was uniform. Increasing the PEO voltage led to porosity increment and formation of the high temperature tetragonal zirconia phase (t-ZrO2). Significant enhancement in tribological properties for coated samples was achieved: under optimum conditions, corresponding to the PEO treatment at 500V for 200s, the coating wear rate of 2.62×10−6mm3N−1m−1 and friction coefficient of 0.22 were recorded that are about 120 and 3 times lower than those for the substrate.
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