Thermogravimetric investigation on oxidation kinetics of complex Ti-Al alloys

The oxidation resistance in air of Ti-48Al-2Cr-2Nb, Ti-48Al-2Nb-0.7Cr-0.3Si, Ti-43.5Al-4Nb-1Mo and Ti-47Al-2Cr-8Nb alloys was investigated in the range of 800-1000 °C. Specimens were machined from the core of bars processed by Electron Beam Melting. Oxidation tests were performed in TGA equipment under isothermal conditions at different temperatures. The composition of the oxide layers was investigated by XRD, SEM-EDS and XPS. Layer exfoliation was observed, starting from different temperatures for the different alloys. When spallation did not happen in a significant extent the oxide layers grew according to a parabolic law. The kinetic rate constants and the activation energies were calculated. These kinetic parameters allowed to assess a rank of oxidation resistance, which can be correlated with the composition of the alloys.