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 Al2O3coatings 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 Al2O3coatings with a thickness of approximately 8μm can be obtained on the Ti-45Al-8.5 Nb alloys by MAO for 600 s.The samples with the Al2O3coatings exhibited better high-temperature oxidation resistance.A minimal weight gain of only 0.396 g/m2after 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 Al2O3coatings and the effect of the MAO parameters are also described.