Surface modification of Ti-45Al-8.5 Nb alloys by microarc oxidation to improve high-temperature oxidation resistance

Microarc oxidation (MAO) electrolysis plasma deposition was used to prepare Al2O3 coatings on Ti-45Al-8.5 Nb alloys to improve high temperature oxidation resistance. The surface and cross-section morphologies before and after high-temperature oxidation, the chemical composition, and the phase identification of the coatings were investigated by scanning electron microscopy (SEM), electron probe microanalyses (EPMA), and X-ray diffraction (XRD). The results show that Al2O3 coatings with a thickness of approximately 8 µm can be obtained on the Ti-45Al-8.5 Nb alloys by MAO for 600 s. The samples with the Al2O3 coatings exhibited better high-temperature oxidation resistance. A minimal weight gain of only 0.396 g/m2 after 100 h oxidation at 900 °C was observed for the coatings formed with a deposition voltage of 400 V and using a duty cycle of 3%. The deposition mechanism of the Al2O3 coatings and the effect of the MAO parameters are also described.