Coating strategies for oxidation resistant high temperature Mo-Si-B alloys
During oxidation exposure of uncoated Mo-Si-B alloys, the formation of a borosilicate layer provides a good oxidation barrier, but below 750°C, the glass is too viscous to flow and cover the entire surface of the sample. On the other hand, above 1200°C, the evaporation rate of B2O3 is high and leads to a fast recession of the alloy. In order to enhance the oxidation resistance, two different coatings were designed by application of a kinetic bias strategy and applied by pack cementation. In one case, a continuous borosilicide coating was developed in which the ratio Si/B is controlled and adapted to the substrate. The second coating is based upon an aluminide (MO 3Al8) that is the result of aluminum pack cementation. During the oxidation, the coatings provide, respectively, a continuous protective borosilicate and a layer of alumina at the surface of the sample and enhanced oxidation resistance.
Rioult, Fabien, Ridwan Sakidja, and John H. Perepezko. "Coating strategies for oxidation resistant high temperature Mo-Si-B alloys." ECS Transactions 3, no. 14 (2007): 113.