Improvement of oxide layers formed by plasma electrolytic oxidation on cast Al-Si 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 (similar to 1.4 times), wear resistance (similar to 3 times) and corrosion resistance (similar to 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.

Automated summary

The incorporation of TiC NPs significantly improved the hardness, effective elastic modulus, wear resistance, and corrosion resistance of the oxide layer, while also increasing the layer thickness. This enhancement was attributed to the chemically inert incorporation of particles and an increase in layer crystallinity.