Oxidation resistance and mechanical properties of Ta–Al–N coatings

• Ta-rich (35–42 at.%) Ta–Al–N coatings crystallized into an f.c.c. phase.
• Ta–Al–N coatings with a high Ta content exhibited a nanohardness of 17–20 GPa.
• As-deposited Ta24Al28N48 was near amorphous and exhibited a hardness of 13.4 GPa.
• Adding Al into the TaN matrix increased the oxidation resistance at 600 °C in air.

Ta–Al–N coatings were prepared using reactive magnetron cosputtering on silicon substrates. The coatings with a high Ta content exhibited a face-centered-cubic structure, whereas the coating with a high Al content exhibited a near-amorphous phase. To determine the oxidation resistance of the Ta–Al–N coatings, annealing treatments were conducted in air at 600–800 °C. Adding Al into a TaN structure increased the oxidation resistance to endure 8-h annealing at 600 °C. Moreover, the Ta35Al15N50 coating exhibited a superior oxidation resistance at 700 °C for 4 h. The material characteristics of the annealed Ta–Al–N coatings were examined through Auger electron spectroscopy and transmission electron microscopy and by using a nanoindentation tester.