A MoSi₂-based composite coating by supersonic atmospheric plasma spraying to protect Nb alloy against oxidation at 1500 °C

A MoSi₂-based oxidation resistant coating was directly deposited on Nb alloy substrate by supersonic atmospheric plasma spraying using pure agglomerated MoSi₂ powders. The as-received coating mostly consisted of h-MoSi₂, t-MoSi₂ and Mo₅Si₃ in a typical layer structure. The cyclic oxidation test of the MoSi₂-based composite coating was evaluated at 1500 °C in air. The formed multi-layer of the coating included SiO₂ outer layer, Mo₅Si₃ + MoSi₂ + SiO₂ middle layer and Nb₅Si₃ transitional layer after oxidation. The results show that the mass loss of the coated sample was 5.31 mg/cm² after exposure at 1500 °C in air for 43 h. The excellent protective ability against oxidation of the MoSi₂-based composite coating could be mainly attributed to a continuous protective SiO₂ scale and an adhesive Nb₅Si₃ diffusion layer, which ensured the low oxygen diffusion rate and the strong bonding to the substrate.