Flexible hard Al-Si-N films for high temperature operation

This article reports on flexible hard Al-Si-N films prepared by reactive magnetron sputtering. The structure and mechanical properties of Al-Si-N films were controlled by the content of Si in the film, partial pressure of nitrogen p_N2 used in sputtering and the power delivered to the magnetron. The Al-Si-N films with a low (≤ 10 at.%) Si content and with a high (≥ 20 at.%) Si content were prepared. Correlations between the structure, microstructure, mechanical properties and their thermal stability of the Al-Si-N films are analyzed in detail. Thermal stability of Al-Si-N films was assessed by thermal annealing in air and water vapor up to annealing temperature T_a = 1200 °C. It is shown that (1) the increase of Si content in the Al-Si-N film leads to the change of its crystalline structure from polycrystalline to X-ray amorphous and (2) the flexible hard Al-Si-N films with high (i) hardness H ≈ 20 GPa, (ii) ratio H/E^⁎ ≥ 0.1, and (iii) elastic recovery W_e ≥ 60% exhibit enhanced resistance to cracking and (3) the thermal stability of Al-Si-N films with a high (≥ 20 at.%) Si content achieves up to T_a ≈ 1200 °C in air and up to T_a ≈ 800 °C in water vapor; here the effective Young's modulus E^⁎ = E / (1 − ν²), E is the Young's modulus and ν is the Poisson's ratio. Conditions under which the flexible hard Al-Si-N films with enhanced resistance to cracking and high thermal stability can be prepared are described in detail.