Mechanism of Al2O3 coating by cathodic plasma electrolytic deposition on TiAl alloy in Al(NO3)3 ethanol-water electrolytes

Barrier layer was prepared on TiAl alloy by Micro-arc oxidation(MAO) technique in silicate electrolyte, and cathodic plasma electrolytic deposition (CPED) technique was used to fabricate Al2O3 ceramic coating on prepared TiAl alloy in Al(NO3)3 (30 g/L) ethanol electrolytes with different water content by volume. Microstructure, composition and properties of coatings were analyzed, and mechanisms of different electrolytes were evaluated. The results showed that both arc-voltage and work voltage decreased with the increase of water content. Al2O3 CPED coatings were composed of deposition particles and cracks, and contained α-Al2O3 phase mainly and a small amount of γ-Al2O3 phase. The organic reaction mechanism was studied and the performance of TiAl alloy with CPED coating under 950 °C was superior to TiAl substrate.