Isothermal oxidation and interdiffusion behavior of MoSi2/WSi2 compound coating on Nb-Ti-Si based alloy

The oxidation and diffusion behaviors of MoSi2/WSi2 compound coating on the Nb-Ti-Si based alloy at 800, 1250 and 1350 degrees C have been investigated. The coating exhibited excellent oxidation resistance at 800 degrees C and 1250 degrees C, and the scale growth rates were about 0.335 mu m(2) h(-1) and 0.939 mu m(2)h(-1), respectively. M 800 degrees C, pesting oxidation was successfully suppressed and formation of Mo5Si3 was mainly resulted from the slow diffusion rate of Si atoms. Therefore, there was no Mo5Si3 at the scale/MoSi2 interface when oxidized at 1250 and 1350 degrees C. At 1250 degrees C, WSi2 layer showed strong restriction against outward diffusion of alloying element atoms. Thus, a pure SiO2-Al2O3 scale about 9.5 mu m thick was obtained after oxidation for 100 h. At 1350 degrees C, the WSi2 layer degraded into porous W5Si3 in situ within a short duration and the outward diffusion was increased. As a result, oxides like Nb2O5, YNbO4 and AlNbO4 formed in the thick scale.