Abstract
To improve the ultra-high temperature oxidation and thermal shock resistance of Nb alloys, we prepared a novel niobium-based oxide protective coating that forms three lines of defense through multi-gradient design. In particular, Nb3B2-NbB2 prevents Si diffusion. WSi2 stores rich Si to generate SiO2. The composite oxide film can heal oxidation defects. The finite element and first-principles calculations results show that multi-gradient coating can radiate heat, relieve interlayer stress and CTE mismatch. The coating forcefully protects the substrate from O2 erosion, so that its oxidation life exceeds 13 h at 1850 ℃, and the thermal shock reaches 600 cycles.
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