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

Abstract

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