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E. Aschauer, P. Felfer, H. Bolvardi, M. Arndt, P. Polcik, P.H. Mayrhofer, H. Riedl:
"Fundamental study of oxygen induced decomposition pathways in PVD deposited TiAlN/Mo-Si-B multilayer coatings";
Talk: EMRS Spring Meeting 2019, Nizza; 2019-05-27 - 2019-05-31.

Severe oxidation in high temperature environments represents a prominent failure mechanism in various protective coating materials. Major aspects in the design of highly oxidation resistant thin films are the formation of a continuous, non volatile and well adherent oxide scale combined with retarded transport kinetics. In principle, oxidation is a diffusion driven process, very often dominated by either of metal atom outward diffusion or oxygen inward diffusion. Therefore, the design of multilayered coating systems including oxygen diffusion barriers - e.g. the implementation of nanocrystalline Mo Si B layers into TiAlN coatings - is a promising approach to impede progressing oxidation.
For a fundamental understanding of oxygen diffusion pathways in combined arc evaporated TiAlN coating with incorporated magnetron sputtered Mo Si B layers, we characterised the as deposited as well as oxidised state (60 min @ 900 °C in O18 as tracer) using atom probe tomography (APT). For the APT analysis, we prepared three horizontal tips (3 positions between the growing scale and the substrate material) in order to detect possible oxygen gradients throughout the multilayer as well as on a very localised level within the single TiAlN and Mo Si B layers.
The data suggests a rapid diffusion along structural defects such as column boundaries within the crystalline TiAlN layers as well as strong accumulations of oxygen within the Mo Si B barriers, strongly retarding the ongoing oxidation process.

Project Head Helmut Riedl:
CDL-SEC