Degradation of Yb–Gd–Ti-Si middle entropy silicides in oxidizing atmosphere

Using arc melting, a novel rare-earth silicide, middle entropy Yb–Gd–Ti-Si, was fabricated for high-temperature material applications. The oxidation behavior of the Yb–Gd–Ti-Si was evaluated through oxidation tests conducted at 1200 °C for 1, 2, 4, and 8 h in air. The oxidation rate at 1200 °C was almost the same, regardless of the addition of Ti. The oxidation rate of Yb–Gd–Ti-Si at lower temperatures (600 °C to 900 °C) was lower than that of Yb–Gd–Si. In addition, detailed microstructural observations indicate that the formation of TiO2 and other oxides in the Yb-Ti–O (Yb–Ti–Si–O) phase suppresses the formation of Yb2O3, causing a drastic oxidation at intermediate temperatures (600 °C to 900 °C). These results indicate that the addition of Ti to Yb–Gd–Si is effective at preventing the preferential oxidation of the grain boundaries at 600 °C to 900 °C, which is commonly observed in metal silicides.