High temperature oxidation behavior of Ti5Si3-based intermetallics

The isothermal oxidation behavior of binary and ternary Ti5Si3 alloy was investigated at 1000 °C in oxygen and nitrogen-containing atmospheres. Several critical issues regarding oxidation of Ti5Si3 at elevated temperatures, including effect of Si, N, and C contents, were examined. Although Ti5Si3 within the homogeneity range can form silica-containing scale in pure oxygen upon high temperature exposure, only Si-rich composition is oxidatively stable in air. Presence of N2 in the atmosphere alters the oxidation behavior of Ti5Si3 at elevated temperature by nucleation and growth of nitride subscale, which prevents the formation of protective silica layer and leads to an accelerated degradation. The initial formation of silica by either pre-oxidation or employing Si-rich composition (i.e. Ti5Si3.2) inhibits the nucleation and growth of nitride subscale, and enhance the oxidation resistance of Ti5Si3 in nitrogen-containing atmosphere at elevated temperatures. C-doped alloys (i.e. Ti5Si3C0.5 and Ti5Si2.8C0.5) possess excellent oxidation resistance in both pure oxygen and in nitrogen-containing atmospheres partially due to increased activity of Si relative to Ti which favors the formation of SiO2 and inhibits the nitride formation beneath the oxide scale.