Effect of Concentration of SiO2 Nanoparticles in the Electrolyte on the Composition and Properties of Oxide Layers Formed by Plasma-Electrolytic Oxidation on Silumin AK7

The effect of additions of SiO2 nanoparticles (the average size 100 nm; the concentration 0.3 and 3 g/liter) into an alkaline-phosphate-silicate electrolyte on the characteristics of the oxide layer formed by plasma-electrolytic oxidation (PEO) on AK7 silumin is studied. The concentration of the nanoparticles is shown to affect nonlinearly the phase composition, the proportion of the amorphous phase, the characteristics of the crystallites (the sizes and the microstresses), the layer thickness and the hardness, the wear resistance, and the corrosion resistance of the oxide layers. The less defective and the thickest layer and the highest protective properties, wear resistance and hardness are observed in the oxide layers formed when the concentration of nanoparticles in the electrolyte is 0.3 g/liter. These layers are also characterized by a minimum fraction of amorphous phase and largest mullite crystallites.