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

Abstract

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 Ti1-x-zAlxSizN 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 Ti1-x-zAlxSizN 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 Ti0.48Al0.46Si0.06N film presents the highest hardness values within the whole studied temperature range (as-deposited, 800–1200 °C). All Ti1-x-zAlxSizN 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 Ti1-x-zAlxSizN films at 800–1000 °C is improved with increasing Si content, due to the suppressed transformation of anatase-to-rutile TiO2 and the promoted formation of a top dense oxide scale. After oxidation at 900 °C for 15 h, the Ti0.54Al0.45Si0.01N film has been completely oxidized, whereas Ti0.53Al0.45Si0.02N, Ti0.51Al0.46Si0.03N, Ti0.48Al0.46Si0.06N and Ti0.45Al0.47Si0.08N 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 Ti1-x-zAlxSizN thin films.