Effect of Si content on the thermal stability and oxidation resistance of arc-deposited TiAlSiN films with cubic structure.

Recently, TiAlSiN thin films have attracted increasing research interest due to their potential to have simultaneously enhanced hardness, thermal stability, and oxidation resistance compared with Si-free TiAlN films. Previous studies have revealed that a relatively low Si content (2.1–6.0 at.% Si) is essential for the phase stability and hardness of TiAlSiN thin films. Despite the optimum Si content for the hardness of TiAlSiN thin films being proposed, a systematical study concerning the optimum Si content for tailored phase stability, thermal stability, and oxidation resistance of TiAlSiN thin films is still missing. Here, we arc-deposited Ti 1-x-z Al x Si z N thin films (x = ~0.45, 0.01 ≤ z ≤ 0.08), and investigated the dependence of their structure, mechanical properties, thermal stability, and oxidation resistance on Si content. XRD analysis reveals the transformation from single-phase cubic structure for z ≤ 0.06 to a cubic-wurtzite dual-phase structure for z = 0.08. Increasing the Si content of cubic-structured Ti 1-x-z Al x Si z N thin films conduces a continuous increase of hardness (H) from 29.3 ± 0.5 GPa for z = 0.01 up to 37.3 ± 0.7 GPa for z = 0.06, whereas the w-AlN formation leads to a drop of H to 32.8 ± 0.6 GPa for z = 0.08. Furthermore, enhancing the Si content from z = 0.01 to z = 0.06 continuously improves film thermal stability, where the Ti 0.48 Al 0.46 Si 0.06 N film presents the highest hardness values within the whole studied temperature range (as-deposited, 800–1200 °C). All Ti 1-x-z Al x Si z N films undergo age-hardening, with peak H of 33.3 ± 1.0 GPa at 1000 °C for z = 0.01, 35.0 ± 0.6 GPa at 1100 °C for z = 0.02, 35.4 ± 0.5 GPa at 1100 °C for z = 0.03, 40.2 ± 0.7 GPa at 1200 °C for z = 0.06, and 37.8 ± 0.6 GPa at 1100 °C for z = 0.08. Additionally, the oxidation resistance of Ti 1-x-z Al x Si z N films at 800–1000 °C is improved with increasing Si content, due to the suppressed transformation of anatase-to-rutile TiO 2 and the promoted formation of a top dense oxide scale. After oxidation at 900 °C for 15 h, the Ti 0.54 Al 0.45 Si 0.01 N film has been completely oxidized, whereas Ti 0.53 Al 0.45 Si 0.02 N, Ti 0.51 Al 0.46 Si 0.03 N, Ti 0.48 Al 0.46 Si 0.06 N and Ti 0.45 Al 0.47 Si 0.08 N films exhibit oxide scales of ~1.7, ~1.4, ~1.2 and ~0.9 μm, respectively. Overall, we propose z = 0.06 as the optimum Si content for the over-rounded performance of Ti 1-x-z Al x Si z N thin films. • TiAlSiN films with close Al content and gradient Si content were deposited by arc evaporation. • Elevated Si content of cubic TiAlSiN films favors the hardness and thermal stability. • Enhancing Si content improves the oxidation resistance of TiAlSiN films. • 6 at.% at metal sublattice is the optimum Si content for the overall performance of TiAlSiN films. [ABSTRACT FROM AUTHOR]