Oxidation Behavior of Germanium- and/or Silicon-Bearing Near-α Titanium Alloys in Air

The effect of germanium (Ge) and/or silicon (Si) addition on the oxidation behavior of the near-α alloy Ti-5Al-2Sn-4Zr-2Mo was investigated in air at 973 K (700 °C). Ge addition decreased the oxidation resistance because of the formation of a Ge-rich layer in the substrate at the TiO₂/substrate interface, enhancing Sn segregation at the interface. In addition, a small amount of Ge dissolved in the external Al₂O₃ layer. These results reduced the aluminum activity at the interface, suppressed the formation of Al₂O_3, and increased the diffusivity of oxygen in the oxide scales. The addition of 0.2 and 0.9 wt pct Si was beneficial for improving oxidation resistance. The effect of germanide and silicide precipitates in the matrix on the oxide growth process was also discussed.