An investigation of the characteristics of Al2O3/TiO2 PEO nanocomposite coating

•Characterizing PEO Al2O3/TiO2 nanocomposite coatings on 7075 Al alloy.•Evaluating and interpreting the corrosion behavior of the coatings in acidic mediums.•Investigating the effects of nanoparticle concentration on the coating properties.•Determining PEO coatings porosity content with a new method. Plasma electrolytic oxidation (PEO) was employed to obtain Al2O3/TiO2 nano-composite coatings. The process was carried out in a silicate base electrolyte in the presence of 0–4gL−1 TiO2 nanoparticles. A DC power supply was used to apply 150mAcm−2 current density for 60min on aluminum samples. XRD analysis on the coated samples revealed that γ-alumina and Mullite were formed in all cases, while TiO2 detected just by the incorporation of TiO2 nanoparticles. Surface and cross-section elemental maps of composite coatings implied that the nanoparticles were uniformly distributed in coatings upper parts. Coatings possessed about 25 and 10% porosity in the absence and presence of nanoparticles, respectively. This showed that the denser coating was formed in the presence of nanoparticles. Electrochemical measurements also revealed that adding nanoparticles increased the corrosion resistance of the coatings by decreasing the corrosion current density to about 3 times. Nano-indentation test results showed the increase of Hardness, Young's modulus, Stiffness and Fracture toughness of Al2O3/TiO2 nano-composite coatings.