Structure and thermomechanical properties of superlattice-stabilized TiNbTaZrSiAlN high-entropy coating.

Stabilizing the phase structure is the prerequisite for obtaining excellent properties of film materials. Here, we construct a multi-layer superlattice structure including high-entropy sublayer to further tailor the structure and properties of Al-containing nitride coating. A fully cubic structure of Ti 0.11 Nb 0.14 Ta 0.13 Zr 0.14 Si 0.09 Al 0.39 N/Ti 0.55 Al 0.45 N (HEN_M) multilayer is realized by stabilizing the cubic/wurtzite-mixed Ti 0.11 Nb 0.14 Ta 0.13 Zr 0.14 Si 0.09 Al 0.39 N (HEN) sublayers with the cubic Ti 0.55 Al 0.45 N template layers. The coherent interface strain increases the hardness to 37.5 ± 1.1 GPa for HEN_M in comparison with the corresponding monolithic coatings with 28.2 ± 0.9 GPa for Ti 0.55 Al 0.45 N and 22.2 ± 0.7 GPa for HEN. Simultaneously, the HEN_M multilayer shows the optimal Vickers indentation toughness. All coatings exhibit age-hardening characteristics stemming from the spinodal decomposition. Compared to Ti 0.55 Al 0.45 N reaching its peak hardness of ∼32.9 ± 0.9 GPa at 900°C, the sluggish diffusion effect promotes HEN and HEN_M maintaining the maximum hardness of ∼25.6 ± 0.8 GPa and ∼39.6 ± 0.9 GPa upon annealing to 1100 and 1000°C, respectively. In addition, exposed to synthetic air at 850°C for 10 h, Ti 0.55 Al 0.45 N coating has been completely oxidized, whereas the HEN and HEN_M coatings only experience partial oxidation with oxide scales of ∼1.52 and 0.78 μm. • TiNbTaZrSiAlN/TiAlN (HEN_M) realizes the epitaxial growth with coherent interfaces. • HEN_M behaves higher hardness and toughness than corresponding monolithics. • HEN_M presents the peak hardness of ∼39.6 ± 0.9 GPa at 1000°C. • HEN_M achieves optimally elevated oxidation resistance. [ABSTRACT FROM AUTHOR]