Influence of siliconizing on the oxidation behavior of plasma sprayed MoSi2 coating for niobium based alloy

• Silicide coating was deposited on Nb-based alloy using a two-step method.
• HAPC treatment can make different roughness for substrate.
• 5 h HAPC could produce best NbSi2 layer compatible with MoSi2 outer layer.
• A proper HAPC plus spraying can result in a good oxidation resistance.

Plasma spraying combined with halide activated pack cementation (HAPC) was used to deposit silicide coating on Nb-based alloy. X-ray diffraction (XRD) and energy disperse spectrum (EDS) indicate the formation of the siliconized NbSi2 transition layer and the sprayed MoSi2 outer layer. NbSi2 layer prepared with HAPC exhibits relatively uneven surface which could promote the deposition of the sprayed MoSi2. The coating specimen with 5 h siliconizing presented the best oxidation resistance with only 0.18% mass gain after 25 h oxidation at 1200 °C in air. The synergistic protection effect, depending on the continuous silica layer formed on the coating surface and the dispersal silica within the coating and interface, is responsible for the excellent oxidation resistance of the coating.