Microstructure and oxidation resistance of TiO2 modified multilayer coating prepared by HAPC/MAO

A TiO2-Nb2O5-SiO2-Al2O3/NbSi2/NbAl3 multilayer coating was prepared on Nb alloys through halide activated pack cementation (HAPC) and micro-arc oxidation (MAO). The multilayer coatings were composed of a TiO2-Nb2O5-SiO2-Al2O3 outer layer, a NbSi2 middle layer and an Al-rich inner layer. The isothermal oxidation resistance of TiO2-Nb2O5-SiO2-Al2O3/NbSi2/NbAl3 multilayer coated Nb alloy was investigated at 1100 and 1200 °C. Besides, the microstructure evolution and element diffusion of the coatings were studied at 1200 °C. The results showed that after 1200 °C oxidation for 50 h, the weight gain of TiO2-Nb2O5-SiO2-Al2O3/NbSi2/NbAl3 coating sample was 8.54 mg/cm2, which was significantly lower than the coating without TiO2. An improvement in the high-temperature oxidation resistance of coating with TiO2 should be ascribed to the formation of continuous and compact oxide scale on the surface.