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.