Isothermal and cyclic oxidation resistance of boron-modified and germanium-doped silicide coatings for titanium alloys
- Ohio State Univ., Columbus, OH (United States)
Since titanium alloys with an adequate balance of mechanical properties and high-temperature oxidation resistance have not been developed, protective coatings are required. In the authors previous paper, B-modified and Ge-doped silicide diffusion coatings grown on Cp Ti, Ti-24Al-11Nb, Ti-22Al-27Nb, and Ti-20Al-22Nb by the halide-activated, pack-cementation method were described. In this study, isothermal and cyclic oxidation were used to evaluate the oxidation performance of these coatings in comparison to uncoated substrates. The rate-controlling mechanism for isothermal oxidation at high temperature was solid-state diffusion through a SiO{sub 2} scale, while the mechanism for low-temperature oxidation involved grain-boundary diffusion through TiO{sub 2}. Both isothermal and cyclic oxidation rates for the B-modified and Ge-doped silicide coatings were much slower than for pure TiSi{sub 2}. Oxygen contamination was not detected by microhardness measurements in the coated substrates after 200 oxidation cycles at 500-1000{degrees}C for the Ti-Al-Nb alloys, or at 500-875{degrees}C for Cp Ti. The excellent oxidation resistance for the optimum coating compositions is discussed.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 283039
- Journal Information:
- Oxidation of Metals, Journal Name: Oxidation of Metals Journal Issue: 5-6 Vol. 45; ISSN OXMEAF; ISSN 0030-770X
- Country of Publication:
- United States
- Language:
- English
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