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 Ti0.11Nb0.14Ta0.13Zr0.14Si0.09Al0.39N/Ti0.55Al0.45N (HEN_M) multilayer is realized by stabilizing the cubic/wurtzite-mixed Ti0.11Nb0.14Ta0.13Zr0.14Si0.09Al0.39N (HEN) sublayers with the cubic Ti0.55Al0.45N template layers. The coherent interface strain increases the hardness to 37.5 ± 1.1GPa for HEN_M in comparison with the corresponding monolithic coatings with 28.2 ± 0.9GPa for Ti0.55Al0.45N and 22.2 ± 0.7GPa 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 Ti0.55Al0.45N reaching its peak hardness of ~32.9 ± 0.9GPa at 900°C, the sluggish diffusion effect promotes HEN and HEN_M maintaining the maximum hardness of ~25.6 ± 0.8GPa and ~39.6 ± 0.9GPa upon annealing to 1100 and 1000°C, respectively. In addition, exposed to synthetic air at 850°C for 10h, Ti0.55Al0.45N 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.