Dual-electrolyte fabrication of micro arc oxidation coatings on Ta-12W alloy with enhanced wear resistance

Electrolyte systems are crucial for the micro-arc oxidation (MAO) process. In this paper, we have prepared MAO coatings on Ta-12W alloy in alkali electrolytes with different concentrations of phosphate and aluminate. The effect of the electrolyte on the composition, morphology, and microstructure of the coating is investigated in detail. It is found that the growth of the coating in phosphate is dominated by the oxidation of the substrate, with numerous crater-like pores on the surface. However, aluminate can greatly promote the growth rate of the coating through the deposition effect of aluminum compounds, along with the pancake-like structure and pro-trusions on the surface. The characterization of the phase structure demonstrates that in the phosphate system, the outer layer of the coating is well crystallized and contains large-sized Ta2O5 crystals, while the aluminate favors the formation of coatings with an inner nanocrystalline layer and an outer amorphous layer. The growth process of MAO coatings in different electrolytes is also discussed. Moreover, the wear resistance of the coating is evaluated and the corresponding wear behavior is studied. The results suggest that the coatings prepared in the dual-electrolyte exhibit superior wear resistance, with the wear rate much lower than that of the substrate.