Improvement of oxide layers formed by plasma electrolytic oxidation on cast AlSi alloy by incorporating TiC nanoparticles

The effect of titanium carbide nanoparticles (TiC NPs) on the structure, chemical and phase composition of the oxide layers obtained by plasma electrolytic oxidation (PEO) on the aluminum-silicon alloy (7.5 wt% Si) was investigated. A significant increase in hardness and effective elastic modulus (~1.4 times), wear resistance (~3 times) and corrosion resistance (~10 times) along with a substantial increase of the layer thickness (about 30%) were found to be connected with chemically inert incorporation of TiC NPs into the oxide layer, while the volume fraction of the incorporated particles in the oxide layer was only about 1%. Improvement of the layer properties was concerned with a decrease in the number of pores and cracks, an increase in the layer crystallinity, and a shift in the phase composition towards more stable phases such as mullite. The assumed mechanism of the TiC NPs effect is a decrease in the breakdown voltage of vapor-gas bubbles (VGB) due to sparking (local breakdowns) from cathodic electrolyte onto the TiC nanoparticles incorporated into the microchannel walls. Sparking to these particles can promote ionization of the gaseous medium, providing earlier microarc discharge through the entire VGB. It results in a substantial increase in the number of microarc discharges, which then initiate larger volumes of melted splash metal and subsequently larger volumes of oxide layer. The higher average temperature results in a decrease in the defectiveness of the macrostructure, the removal of gas from the layer, the growth of crystallites, the removal of residual strains, and a stabilization in the phase composition. [Display omitted] •PEO coating was formed on AlSi alloy under the adding TiC NPs into electrolyte.•TiC NPs demonstrated inert mechanism of incorporation into the coating during PEO.•Incorporation of TiC NPs increased hardness, wear and corrosion resistance.