High-temperature oxidation resistance of ceramic coatings on titanium alloy by micro-arc oxidation in aluminate solution

Ceramic coatings with aluminum titanuate (Al2TiO5) were prepared on Ti-6Al-4V alloy using pulsed bi-polar Micro-arc Oxidation (MAO). The micromorphology and phase composition of the micro-arc-oxidition ceramic coatings on the titanium alloy were characterized by X-ray powder diffraction (XRD), and scanning electron microscopy (SEM) respectively. The results revealed that the distinct discharge channels and pores on the surface of the micro-arc-oxidition coatings appeared, and these channels were connected in the molten state. The electrolyte concentration was inversely proportional to the coating hardness; additionally, the coating prepared with sodium aluminate and sodium hypophosphite concentrations of 4 g/L and 0.5 g/L, respectively, was the most refined after high-temperature sintering, and it was demonstrated to better prevent oxidation. Increasing the electrolyte concentration coincided with fluctuating coating thermal shock resistance. The thermal shock resistance of the coating respectively prepared with sodium aluminate, and the sodium hypophosphite concentrations of 4 g/L and 0.5 g/L was the highest. Additionally, the high-concentration coatings performed significantly better than the low-concentration coatings. The oxidation resistance of the coating samples was also significantly higher than that of the TC4 titanium alloy substrate. The adhesion strength between the coatings and the substrate with and without the sealing treatment was measured by tensile tests. Then, the high-temperature oxidation performance of the coating samples with and without the sealing treatment was investigated by conducting a hightemperature oxidation experiment at a calcinating temperature of 500 degrees C. The results indicate that the adhesion strength between the coatings and substrate was high for the as-prepared and sealed micro-arc oxidation samples regardless of whether they were calcined. The high-temperature oxidation mass increase curves for the sealed and unsealed coating samples calcined at 500 degrees C for 500 h revealed that the high-temperature-oxidationinduced mass increase of the coating samples sealed with a sodium silicate solution was much lower than that of the titanium alloy substrate. Thus, the sealing treatment significantly improved the high-temperature oxidation resistance of the TC4 titanium alloy. Lastly, the high-temperature oxidation behavior at 500 degrees C was analyzed and discussed.

Automated summary

The study found that ceramic coatings with aluminum titanuate prepared using pulsed bi-polar micro-arc oxidation on titanium alloy exhibited distinct discharge channels and pores, and demonstrated good oxidation resistance at high temperatures. The hardness of the coatings was inversely proportional to the electrolyte concentration, with higher concentration coatings showing better thermal shock resistance and oxidation resistance compared to lower concentration coatings.