H. Guleryuz, H. Cimenoglu, Istanbul Technical University, Istanbul, Turkey

Summary:

Titanium and its alloys are outstanding materials for aerospace components due to their high strength, low density and good corrosion resistance. They are used both in aircraft engines and airframe construction. Typical applications are forged landing gear components, wing leading edges, fire bulkheads, structural parts and rotors for helicopters. They are also used to a very great extent in the construction of aircraft gas turbine engines. Guide vanes and rotor blades, discs and casing parts of jet engine compressors are significant examples. However, poor oxidation resistance limits their use at elevated temperatures. Oxidation not only results in thinning of the material due to oxide layer formation at the outer surface but also degrades the mechanical properties due to formation of brittle alpha case beneath the oxide layer.

In the present study, oxidation of Ti-6Al-4V alloy, which is the most widely used titanium alloy, has been examined over the temperature range of 600-800°C. The results showed that the oxidation rate obeyed parabolic kinetics below 700°C and linear kinetics above 700°C. However, brittle alpha case depth obeyed parabolic kinetics through the entire temperature range and yielded the activation energy of 200 kJ/mol. According to the results of the experiments, temperature compensated time parameter has been proposed on the basis of Sherby-Dorn approach to predict the extent of alpha case depth.