As an important ultra-high temperature structural material,Nb-Si based alloys boast advantages of high melting point,low density,and excellent high-temperature performance,making them promising candidates for aerospace sector. However,the poor high-temperature oxidation resistance significantly hinders the development of Nb-Si based alloys. Silicide coatings can effectively enhance the high-temperature oxidation resistance of Nb-Si based alloys. Y and Y2O3 modified Mo-Si-B coatings were prepared on the surface of Nb-Si based alloys with the laser cladding technique. The Y/Y2O3 modified Mo-Si-B coatings mainly consist of t-MoSi2,h-MoSi2,Mo5Si3,and a small amount of MoB2. The addition of Y promotes the diffusion of elements within the Mo-Si-B coating,resulting in a more uniform distribution of chemical composition and microstructure,a reduction in the size of MoSi2 phase,and an increase in the proportion of eutectic structure. In contrast,the Y2O3 modified Mo-Si-B coating contains a significant amount of Mo5Si3 phase and exhibits considerable dilution effects from the substrate. After oxidation at 1250 ℃ for 60 hours,a continuous and dense oxide layer is formed on the surface of the Mo-Si-B coating,predominantly composed of borosilicate. The addition of Y enhances the formation of oxide layer on Mo-Si-B coating surface and significantly improves its oxidation resistance at high temperatures. However,the Y2O3 modified Mo-Si-B coating tends to generate non-protective metal oxides during the oxidation process. Compromising the continuity of borosilicate glass phase,it ultimately generate decreased high-temperature oxidation resistance for the coating containing Y2O3.
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