EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The field of turbine blades in aeronautical jet engines is dominated by nickel-based superalloys, due to their ability to withstand highly demanding mechanical and thermal loads. From the environmental perspective, reducing weight and enhancing efficiency, the main disadvantage of nickel-based superalloys is their high density of 8 g/cm³. As an alternative, lightweight intermetallic $\gamma$-TiAl based alloys have been extensively investigated in order to allow their commercial implementation in aerospace and automotive industries. The first TiAl application in turbine engines was made by General Electric (GE), employing their TiAl alloy 48-2-2 for the low-pressure turbine blades. Afterwards, a new beta-stabilized TiAl alloy, named TNM, was successfully developed and also used to manufacture low-pressure turbine blades. The improved workability of the TNM alloy allows its use up to 750ºC; above that temperature, its use is still impeded by insufficient oxidation resistance. In order to increase the operation temperature of TiAl alloys, the investigation and understanding of the relationship between their thermo-mechanical properties and microstructure is required. In the current work, in addition to a detailed microstructural characterization, a thermophysical analysis on these well-known engineering TiAl alloys, GE 48-2-2 and TNM, has been carried out. This study consists on directional spectral emissivity measurements between 150ºC and the working temperature under vacuum and includes an isothermal oxidation in air at 850ºC. The oxidation properties and behavior have been analyzed and compared for the both mentioned alloys. Additionally, the results of directional spectral emissivity measurements have been integrated to calculate the total hemispherical emissivity, which is the key heat transfer parameter in the high-temperature high-vacuum environments such as additive manufacturing.