Synergistic effects of Ta and Si alloying on the long-term oxidation resistance of Ti1-xAlxN coatings

Ti-Al-N coatings are emerging as robust stand-alone protective solutions in turbine applications. To maximize their potential in high-temperature environments, improving their long-term oxidation stability is key. In this work, we investigate the combined effect of Ta and Si alloying on the oxidation of thick (8 to 15 μm) cathodic arc evaporated Ti 1-x-y-z Al x Ta y Si z N coatings at 850 °C up to 500 h. Combined Ta and Si alloying yields extremely low oxidation kinetics following a logarithmic rate law, demonstrating exceptional long-term stability. After 500 h, the oxide scale thickness decreases from ~1.1 μm for the low-Al Ti 0.49 Al 0.36 Ta 0.13 Si 0.02 N coating to <600 nm for the high-Al Ti 0.40 Al 0.45 Ta 0.13 Si 0.02 N variant. Correspondingly, the logarithmic rate constants lie between 0.379 ± 0.019 μm × h −1 (Ti 0.49 Al 0.36 Ta 0.13 Si 0.02 N) and 0.243 ± 0.020 μm × h −1 (Ti 0.40 Al 0.45 Ta 0.13 Si 0.02 N), indicating a combined impact of Ta and Si in relation to the Al content on the oxidation kinetics. Detailed cross-sectional TEM analyses reveal a multilayered oxide scale consisting of two inner Ti-Ta-Si-containing sublayers and an outer Al 2 O 3 layer. The findings demonstrate that Ti 1-x-y-z Al x Ta y Si z N coatings significantly outperform conventional Ti-Al-N in the long-term oxidation regime, where the combined effects of Ta and Si emerge as the decisive factor for retarded oxygen inward diffusion. • Cathodic arc evaporation of mixed Ta and Si alloyed Ti 1-x Al x N-based thin films. • Ti 1-x-y-z Al x Ta y Si z N exhibits exceptional oxidation resistance up to 500 h at 850 °C. • Ti 0.40 Al 0.45 Ta 0.13 Si 0.02 N low (highest Al) exhibits the slowest oxidation kinetics.