Abstract
Spent MoSi2 heating elements were used to fabricate MoSi2, ZrB2/MoSi2 and MoSi2-ZrB2/MoSi2 oxidation resistant coatings via a two-step process of slurry painting and spark plasma sintering. Cracks appeared in simple MoSi2 and ZrB2/MoSi2 coatings, whilst MoSi2-ZrB2/MoSi2 coating was crack-free as CTE mismatch was reduced. Mo5Si3 and MoB diffusion layers formed under MoSi2-ZrB2 transition layer in MoSi2-ZrB2/MoSi2 coating, revealing good metallurgical combination between the substrate and coating. On one side the silica layers covering MoSi2 and ZrB2/MoSi2 coatings displayed diffused cracks after oxidation at 1773 K for 100 h, on the other side it was dense and continuous for MoSi2-ZrB2/MoSi2 coating, showing low oxidation rate constant at 1773 K. Furthermore, MoSi2-ZrB2 transition layer in MoSi2-ZrB2/MoSi2 coating possessed good short-term oxidation protective properties at 1873 and 1973 K since the formation of ZrSiO4 improved the stability of Si-O-Zr composite oxide scale and diminished the oxygen permeability, therefore demonstrating good high-temperature oxidation resistance.
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