Ultra-High Oxidation Resistance of Nano Structured Thin Films

Abstract

Diffusion driven high-temperature oxidation is one of the most important failure mechanisms of protective thin films in industrial applications. Within this study, we investigated the diffusion of oxygen at 800 to 1100 °C through nano-laminated crystalline Ti Al N and amorphous Mo Si B based multilayer coatings. Combining 18O tracer diffusion with atom probe tomography was used for identifying the most prominent oxygen diffusion pathways and hence weakest points for oxidation. An oxygen inward diffusion along column boundaries within Ti-Al-N layers in front of a visually prevalent oxidation front could be proven, highlighting the importance of these fast diffusion tracks. Furthermore, the amorphous Mo Si B layers act as barriers and therefore mitigate the migration of oxygen by accumulating attacking O species at a nanoscale range. Preventing oxygen diffusion along column boundaries - through the utilization of amorphous interlayers - lead to paralinear oxidation behavior and stable scales even after 7 h at 1100 °C. Our results provide a detailed insight on the importance of morphological features such as grain and column boundaries during high-temperature oxidation of protective thin films, in addition to their chemistry.