1. School of Materials Science and Engineering, Central South University, Changsha 410083, China
2. State Key Laboratory of Powder Metallurgy, Central South University,Changsha 410083, China
Multi-principal element high-entropy materials (MPE-HEMs) have practically infinite chemical composition space, and their microstructures can also be effectively controlled by synthesis and processing technologies. Therefore, through the coupling design of chemical composition and microstructure, various mechanisms can be effectively coordinated in MPEHEMs to achieve excellent comprehensive mechanical properties. In addition to the strengthening and toughening effects in traditional single-principal element materials, unique mechanisms can be activated in MPE-HEMs to obtain better combinations of strength and ductility/toughness. This overview paper summarizes a variety of unique strengthening and toughening mechanisms in MPE-HEMs, including massive substitutional and interstitial solid solution, metastable engineering and bidirectional transformation, symbiotic dualnanoprecipitation and hierarchical nanoprecipitation, high-stress twinning, high-density stacking faulting and sluggish martensitic transformation, and nanoamorphous-crystalline high-entropy composite mechanisms. The principles and ideas for designing compositions and microstructures of MPE-HEMs to realize the above unique mechanisms are described, the microscopic fundamentals of the typical mechanisms in specific MPE-HEMs are also analyzed. Furthermore, based on the classical strengthening and toughening mechanisms in traditional single-principal element materials and the uniqueness of MPE-HEMs, other possible strengthening and toughening mechanisms are discussed. Finally, the potential of MPE-HEMs for simultaneously achieving excellent mechanical properties and other functional properties based on the large room of compositional and structural design are prospected, which suggests important ways to effectively exploit the unique advantages and values of MPE-HEMs.