Carbon stoichiometry and mechanical properties of high entropy carbides

The search for new materials via compositional exploration has recently led to the discovery of entropy stabilized and high entropy ceramics. The chemical diversity in the cation sublattice of high entropy ceramics has led to many enhanced properties and applications such as reversible energy storage, low temperature water splitting, amorphous-like thermal transport in crystalline solids and enhanced mechanical properties. This work describes the synthesis and mechanical properties of high entropy (HfNbTaTiZr)C-x thin films as a function of carbon content. The nature of the bonding and microstructure evolves as the material transforms from metallic to ceramic to nanocomposite with variations in the quantity and types of carbon, yielding large variations in the film hardness. Through multiple characterization techniques and first principles investigations, we separate the roles of microstructure and bonding characteristics in the mechanical property development of (HfNbTaTiZr)C-x thin films. This study presents a strategy to establish the bonding, structure, and property relationships in chemically disordered high entropy ceramics, largely based on the relative populations of filled or empty antibonding states for which there are new abilities to do so in high configurational entropy systems that exhibit high solubility of diverse cations while retaining rocksalt structure. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

High entropy ceramics discovered through compositional exploration exhibit enhanced properties and diverse applications. This study investigates the synthesis and mechanical properties of high entropy (HfNbTaTiZr)C-x thin films as a function of carbon content, revealing the evolution of bonding and microstructure with variations in carbon, leading to significant changes in film hardness. Through characterization techniques and first principles investigations, the roles of microstructure and bonding characteristics in mechanical property development of (HfNbTaTiZr)C-x thin films are elucidated.