Exploring nanomechanical characteristics of (CoCrFeMnNi)100-xNx high-entropy nitride ceramics: An integrated experimental and computational approach

High-entropy ceramics (HECs) have recently gained significant attention as promising coating materials for extreme environments due to their excellent mechanical and thermal properties. Despite numerous studies on HECs, there is limited research characterizing the intrinsic mechanical properties based on CoCrFeMnNi equi-atomic composition, also known as the Cantor alloy, one of the most representative high-entropy alloy (HEA) system. This gap arises because the carbon- and nitrogen-affinitive Cr elements tend to form chromium carbides or chromium nitrides, which interfere with evaluations of their intrinsic properties due to the presence of precipitates or initial cracks. In this study, we successfully synthesized crack- and precipitate-free crystalline (CoCrFeMnNi)₈₅N₁₅ and (CoCrFeMnNi)₇₀N₃₀ HECs on the micrometer-scale. Their mechanical properties were evaluated through nanohardness tests, showing higher nanohardness values compared to the CoCrFeMnNi HEA. Furthermore, density functional theory (DFT) calculations were employed to analyze how nitrogen atoms are incorporated into the CoCrFeMnNi metallic lattices and how the transformation into HECs enhances the mechanical properties. The successful fabrication strategy of crystalline CoCrFeMnNi-based HECs, analyses of their microstructures and intrinsic mechanical properties, and the exploration of their underlying mechanisms through DFT calculations, will provide innovative perspectives, spanning from fundamental knowledge to practical applications, for various HEC systems.