Recycling MoSi2 heating elements for preparing oxidation resistant multilayered coatings

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.