Defects in medium-and high-entropy materials: a review

Abstract Medium- and high-entropy materials (M/HEMs) contain at least three principal elements with equal or near-equal fractions, thus representing the unexplored middle parts of phase diagrams. These substances include both metallic and ceramic materials. M/HEMs exhibit outstanding mechanical and functional properties which predestinate them as candidate materials for improved practical applications. Since the lattice defects may influence the performance of M/HEMs, it is worth studying whether the behavior of point defects, dislocations, planar faults and grain boundaries differ from those in traditional substances. Therefore, the present comprehensive review summarizes the existing knowledge on the lattice defects in M/HEMs. The influence of the processing method and the chemical composition on the type and density of defects is overviewed. Special sections are devoted to M/HEM films and bulk high-entropy ceramic materials. In addition, the effect of lattice defects on the mechanical and functional properties of M/HEMs is studied. This is the first comprehensive review in the literature that summarizes the existing knowledge on lattice defects in a very wide range of M/HEMs, including bulk metallic materials, thin films and ceramics.