Thermal stability and oxidation behavior of (V,Al)(O,N) and (Cr,Al)(O,N) thin films

• Applicants: Dr.-Ing. Marcus Hans; Professor Jochen M. Schneider, Ph.D.
• Subject Area: Coating and Surface Technology ; Synthesis and Properties of Functional Materials
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 515702322

Incorporation of oxygen into metastable cubic transition metal (TM) aluminum nitride protective thin films has recently attracted attention. It has been demonstrated that the incorporation of 15 at.% oxygen in (Ti,Al)(O,N) increases its thermal stability compared to (Ti,Al)N as higher temperatures are required to enable mobility on the non-metal sublattice and trigger wurtzite phase formation. However, the effect of chemical composition variations on the thermal decomposition pathways and the oxidation resistance of (V,Al)(O,N) as well as (Cr,Al)(O,N) have not been explored systematically. Consequently, the underlying mechanisms at the near-atomic scale have not been understood. Morever, currently a comparative dataset of thermal decomposition onset temperatures as well as oxidation kinetics for (TM,Al)(O,N) is not available. In this project, single-phase metastable cubic (TM0.5Al0.5)(OyN1-y) thin films with TM = V, Cr and y = 0, 0.2, 0.4 will be synthesized by high power pulsed magnetron sputtering. These films will be annealed in vacuum as well as ambient air and characterized by ion beam analysis, diffraction, nanoindentation, microscopy as well as tomography. This strategy allows to understand relevant mechanisms for thermal decomposition and oxide scale formation. The complete dataset of onset temperatures of thermal decomposition as well as temperature- and time-dependent oxidation kinetics will allow a straightforward and systematic comparison between the different (TM0.5Al0.5)(OyN1-y) thin films with TM = V, Cr and y = 0, 0.2, 0.4. Consequently, three exciting research questions (RQ) will be addressed: RQ1 What mechanisms limit the thermal stability of sputtered (V0.5Al0.5)(OyN1-y) and (Cr0.5Al0.5)(OyN1-y) with y = 0, 0.2, 0.4? RQ2 What mechanisms define the composition-dependent oxidation behavior of (V0.5Al0.5)(OyN1-y) and (Cr0.5Al0.5)(OyN1-y) with y = 0, 0.2, 0.4? RQ3 Is spinodal decomposition a necessary prerequisite for wurtzite phase formation in (TM0.5Al0.5)(OyN1-y) with TM = V, Cr and y = 0, 0.2, 0.4? The key of this project is the use of advanced characterization techniques including electron microscopy tomography for evaluation of the oxide scale formation as well as correlative transmission electron microscopy and atom probe tomography for knowledge of the structural and compositional evolution at the near-atomic scale. Thereby, we aim to advance our understanding of the mechanisms controlling the thermal stability as well as the temperature- and time-dependent oxidation behavior of (V0.5Al0.5)(OyN1-y) and (Cr0.5Al0.5)(OyN1-y) thin films with y = 0, 0.2, 0.4. It is anticipated that the here obtained knowledge from a comparative dataset will enable the future design of coating materials with enhanced thermal and chemical stability.

• DFG Programme: Research Grants