DEVELOPMENT OF OXIDATION RESISTANT TITANIUM ALLOYS BY NIOBIUM ADDITION

The application of titanium alloys is limited to 550°C due to their poor oxidation resistance. It is known that the addition of niobium improves the oxidation resistance of titanium whereas elements like vanadium do not support titanium’s oxidation behaviour. Hence, the underlying mechanisms are not understood. In the present study, different binary titanium-niobium and titanium-vanadium alloys as well as commercially pure titanium were investigated. Oxidation experiments were carried out at 800°C up to 288 hours followed by metallographic analyses to study the oxide layer morphology as well as the microstructure at the interface. Energy-dispersive X-ray spectroscopy mappings (EDS) were used to identify possible changes in the distribution of the alloying elements. In addition, micro-focused hard X-ray experiments have been performed to layer-wise analyse the phase composition in selected samples. As expected, the niobium containing alloys show a better oxidation performance compared to CP-titanium and the titanium-vanadium alloys. The oxide layer consists of TiO2 and Ti2O3. Depending of the niobium content, a niobium-rich layer developed below the metal-oxide-interface hindering oxygen diffusion into the titanium matrix. Based on these results, the minimal niobium content needed for improved oxidation was identified so that oxidation resistant alloys of technical relevance can be developed.