Increased thermal stability of Ti-Al-N thin films by Ta alloying

► Ab initio results show a lower energy of formation with increasing Ta content in Ti-Al-Ta-N. ► Ab initio results show an increasing bonding strength with increasing Ta content in Ti-Al-Ta-N. ► Experiments show that w-AlN forms at 200-300 °C higher Ta with increasing Ta content in Ti-Al-Ta-N. ► Ta free Ti-Al-N coatings fully oxidize during annealing in ambient air at 850 and 950 °C for 20 h. ► 3 at.% Ta in Ti-Al-Ta-N effectively protect against oxidation at similar annealing conditions.