The oxidation behavior of three Nb-Si-based alloys were evaluated at intermediate (800 °C) and high (1250 °C) temperatures for 100 h in air. At 800 °C, the Nb-24Ti-15Si-13Cr-2Al-2Hf (at. %) alloy suffered from catastrophic pest oxidation. This pest phenomenon was suppressed by the addition of Sn. However, Ta addition protected the Nb-Si-based alloys from pest oxidation for a short time. At 1250 °C, Sn could enhance the oxidation resistance of Nb-Si-based alloys due to the formation of a Sn-rich layer. In addition, the oxidation mechanisms of Nb-Si-based alloys at intermediate and high temperatures were discussed.

The MoSi₂-ZrB₂ coatings were prepared on Nb-Si based alloy by atmospheric plasma spraying with the spraying power 40, 43 and 45 kW. The effect of spraying power on the microstructure and oxidation resistance of MoSi₂-ZrB₂ coating at 1250 °C were studied. The results showed that the main constituent phases of coatings were MoSi₂ at all spraying power. The coating became more compact as the spraying power increased. The coating prepared at 45 kW was dense and uniform, which exhibited the best oxidation resistance due to the formation of a dense and uniform glass layer consisting of SiO₂ and ZrSiO₄.

In this study, B modified silicide coatings were prepared on Nb-Si based alloy with Al₂O₃ or SiO₂ inert-filler by pack cementation technology. Both coatings primarily consisted of a (Nb,X)Si₂ with a (Nb,X)B₂ + (Nb,X)Si₂ outer layer. After oxidation at 1250 °C for 100 h, the coatings showed good oxidation resistance due to the formation of a dense silica. The oxidation products of the coating prepared with Al₂O₃ inert-filler consisted of SiO₂, TiO₂ and Cr₂O₃, while that of the coating prepared with SiO₂ inert-filler consisted of SiO₂, TiO₂, Cr₂O₃, and HfO₂. The different oxidation products may be due to the different oxidation process of these two sample at initial oxidation stage.