Empirical Analysis of Lifetimes for Disilicide Coatings on a γ-TiAl Intermetallic Compound

Abstract

The NbSi₂/Nb/γ-TiAl and NbSi₂/Nb functionally graded materials (FGMs) were prepared and their tolerances tested by exposing them to temperatures from 1323 K to 1523 K under vacuum and in air. Oxygen resistivity was estimated from metallographic investigations. The FGM lifetime was estimated by using a diffusion equation that considers the disappearance of the NbSi₂ and Nb interlayer. These occurred during NbSi₂ oxidation and Si diffusion from NbSi₂ to Nb and interdiffusion between Nb and γ-TiAl. The results were validated by diffusion equations. The results indicate that a coating used at 1323 K for 380 h requires a NbSi₂+Nb coating thickness of more than 77 μm.