Lattice Distortion Enhanced Hardness in High‐Entropy Borides

Abstract Revealing the hardening mechanisms is crucial for facilitating the design of superhard high‐entropy borides. Taking high‐entropy diborides (HEB₂) as the prototype, the hardening mechanisms of high‐entropy borides are thoroughly investigated. Specifically, the equiatomic 4—9‐cation single‐phase HEB₂ ceramics (4—9HEB₂) are fabricated by an ultra‐fast high‐temperature sintering method. The experimental results show that the hardness of the as‐fabricated 4—9HEB₂ samples has an increasing tendency with the increase of metal components. With a combination of first‐principles calculations, machine‐learning‐potential‐based molecular dynamics simulations, and scanning transmission electron microscopy characterizations, lattice distortion is explicitly identified to be essential in hardening HEB₂ by increasing strain field fluctuation, enlarging atomic strain energy, and strengthening B─B bonds. The results unravel the hardening mechanisms of HEB₂ by intensifying lattice distortion, providing fascinating guidance for developing superhard high‐entropy borides.