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S. Kagerer, O Hudak, M. Schloffer, H. Riedl, P.H. Mayrhofer:
"TGO formation and oxygen diffusion in Al-rich gamma-TiAl PVD-coatings on TNM alloys";
Scripta Materialia, 210 (2022), 114455; 1 - 5.

γ-TiAl alloys have gained much attention due to their low density, excellent fatigue resistance, and high specific strength at elevated temperatures. Throughout this study, we showcase physical vapor deposited Al-rich γ-TiAl coatings as a considerable solution to extend the durability and longevity of γ-TiAl bulk materials in high temperature regimes (> 750 °C). In detail, the oxidation resistance is enhanced up to at least 850 °C for 1000 h, whilst exhibiting a maximum oxygen affected area of 8.4 µm (16 µm coating). Based on various oxidation treatments (800, 850, and 900 °C), we estimated a mean parabolic rate constant of about 1.03∙10−10 cm²/h and a logarithmic oxygen inward diffusion rate of approximately 1.20∙10−4 cm/h. The corresponding activation energies validate the considerably retarded oxide scale kinetics - particularly, for the thermally grown oxides. Furthermore, the thermal exposure introduced excellent intermixing between the Al-rich γ-TiAl coating and γ-TiAl bulk material, resulting in a coalescence of the coating-substrate interface.

Oxidation resistance; γ-TiAl; TNM; Diffusion coefficients; PVD; Protection coatings

http://dx.doi.org/10.1016/j.scriptamat.2021.114455

https://publik.tuwien.ac.at/files/publik_304057.pdf