High Temperature Oxidation of Γ-Tial‐Based Alloys: Effect of Zirconium

Abstract

Oxidation resistance is a crucial factor for structural high temperature materials. Hence, newly developed alloys must be tested before any high temperature application. Intermetallic titanium aluminides are promising alloys due to their good specific strength and creep resistance at elevated temperatures. Advanced γ-TiAl based alloys are already used as blades in the last stages of the low-pressure turbine of commercial aero engines, where the temperature can reach up to 800°C. This temperature causes pronounced oxidation in γ-TiAl based substrates due to the formation of a non-protective mixed oxide scale. Generally, despite an Al content of more than 40 at.%, binary titanium aluminides form a mixed scale of Al- and Ti-oxides rather than a protective alumina layer, in contrast to iron or nickel aluminides. Therefore, protective measures e.g., alloying with additional elements, must be undertaken. The oxidation behavior of several Zr-containing γ-TiAl based alloys at 900°C in air is reported in this paper. Hereby, the performance of these newly developed alloys (Zr-content 0 – 8.0 at.%) is compared with the TiAl 4822 alloy (Ti-48Al-2Cr-2Nb, in at.%) and the TNM B1 alloy (Ti-43.5Al-4Nb-1Mo-0.1B, in at.%). During isothermal testing in air, mixed scales develop on all untreated samples but with different scale compositions and thicknesses. Thermal cycling leads to spallation of most parts of the scale. This is a crucial factor because the attack is accelerated within areas where the scale has spalled off. The amount of spallation differs between the individual alloys. The results of isothermal as well as thermocyclic exposure tests are presented and discussed in the view of chemical composition and microstructure of the investigated γ-TiAl based alloys.

Keywords: Intermetallics (aluminides), Oxidation, Aero-engine components, Automotive uses, including engines (and other transportation uses)