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 _0.11Nb _0.14Ta _0.13Zr _0.14Si _0.09Al _0.39N/Ti _0.55Al _0.45N (HEN_M) multilayer is realized by stabilizing the cubic/wurtzite-mixed Ti _0.11Nb _0.14Ta _0.13Zr _0.14Si _0.09Al _0.39N (HEN) sublayers with the cubic Ti _0.55Al _0.45N 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 _0.55Al _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 _0.55Al _0.45N 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 _0.55Al _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.