Nickel-based superalloys currently dominate the field of turbine blades in aircraft engines due to their excellent thermo-mechanical properties at high temperatures such as high mechanical strength, good creep response and corrosion resistance. The main drawback of these superalloys, related to  environmental impact, is their high density, which is around 8 g/cm3. This fact has promoted the study and development of the γ-TiAl intermetallics, with a density of 3.9-4.2 g/cm3, as an alternative. In this vein, a new beta-stabilized TiAl alloy with a microstructure composed of γ + \alpha₂+ β₀ ordered phases, named TNM, was successfully developed and implemented in low-pressure turbine blades [1]. The TNM alloy can be employed up to 750ºC; above that temperature, its employment is still impeded by insufficient oxidation resistance. The relationship between the thermo-mechanical properties and microstructure of those TiAl alloys has been extensive  studied [2], but the optical properties in relation to its microstructure have hardly been investigated [3].

In the current work, in addition to a detailed microstructural characterization, a thermo-optical analysis on TNM alloy has been carried out. This study consists on directional spectral emissivity measurements between 200ºC and their working temperature (750-850ºC) under vacuum. In addition, spectral emissivity measurements during isothermal oxidation in air at 850ºC and 750ºC have been performed. The evolution of the interferential peaks in the emissivity during the isothermal oxidation allows us to follow an apparent oxide layer growth as a function of time. Once the material becomes opaque due to the oxidation, directional spectral emissivity measurements have been conducted at 850ºC temperature in air and a total hemispherical emissivity value of 0.72 ± 0.01 has been determined. This total hemispherical emissivity is the key parameter that governs the heat transfer at high-temperature.