Oxidation-resistant boron- and germanium-doped silicide coatings for refractory metals at high temperature

Owing to the poor oxidation resistance of titanium alloys at high-temperature, a protective coating is required. Alloying titanium with enough aluminum or silicon to form a protective Al2O3 or SiO2 scale is not a viable approach. In this study, boron- and germanium-doped silicide coatings were grown on commercially pure (CP) titanium and orthorhombic-base Ti-20Al-22Nb and Ti-22Al-27Nb alloys by a halide-activated, pack cementation method. Isothermal and cyclic oxidation testing in air were used to evaluate the coated substrates at 500–1000 °C. Microhardness profiles were made to test for oxygen contamination of the substrate. These coatings both provided excellent oxidation resistance for CP Ti and the TiAlNb alloys.