High temperature oxidation behavior of MoSi2–Al2O3 composite coating on TZM alloy.

A novel MoSi 2 –Al 2 O 3 composite coating was prepared on Mo-based TZM alloy by slurry sintering method. The oxidation behavior of the coating was evaluated at 1600 °C in static air. Microstructure and phase composition of the as-prepared and oxidized coatings were characterized, and the antioxidant mechanism of the coating at high temperature was discussed. A three-layer structure was observed in the as-prepared coating, consisting of a ∼2 μm thick Mo 5 Si 3 diffusion layer, a ∼65 μm thick MoSi 2 inner layer and a ∼36 μm thick outer layer of mixture of MoSi 2 and Al 2 O 3. After oxidation at 1600 °C for 5 h, all MoSi 2 phases were completely converted to intermediate silicide Mo 5 Si 3 by solid-state diffusion, and the formed Mo 5 Si 3 phase would be transformed into Mo 3 Si phase with further extending the oxidation time. Furthermore, a dense oxide layer of SiO 2 -mullite was formed on the specimen surface, which can effectively protect the material to further oxidation. The MoSi 2 –Al 2 O 3 coating could protect the substrate effectively at 1600 °C for 20 h without failure. The enhanced oxidation resistance of MoSi 2 –Al 2 O 3 coating is due to the formation of multi-layer structure containing a SiO 2 -mullite composite oxide outer layer with high thermal stability and low oxygen permeability. [ABSTRACT FROM AUTHOR]