Abstract
The oxidation and diffusion behaviors of MoSi2/WSi2 compound coating on the Nb-Ti-Si based alloy at 800, 1250 and 1350 °C have been investigated. The coating exhibited excellent oxidation resistance at 800 °C and 1250 °C, and the scale growth rates were about 0.335 μm2 h−1 and 0.939 μm2 h−1, respectively. At 800 oC, 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 °C. At 1250 °C, WSi2 layer showed strong restriction against outward diffusion of alloying element atoms. Thus, a pure SiO2-Al2O3 scale about 9.5 μm thick was obtained after oxidation for 100 h. At 1350 °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.
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