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.