Abstract
During oxidation exposure of uncoated Mo-Si-B alloys, the formation of a borosilicate layer provides a good oxidation barrier, but below 750{degree sign}C, the glass is too viscous to flow and cover the entire surface of the sample. On the other hand, above 1200{degree sign}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 (Mo3Al8) 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.