Applications of powder metallurgy technology in high-entropy materials

High-entropy materials (HEMs) designed with a new material design philosophy have recently emerged as a new type of advanced materials. In contrast to traditional alloys where one or two elements dominate the structural composition, HEMs comprise multiprincipal metallic or metalloid elements, generally ≥5 and in equiatomic or near-equiatomic ratios, thereby possessing high mixing entropy and generally forming a single-phase solid solution structure during solidification process. Because of their unique atomic structures, HEMs exhibit excellent properties such as high strength, hardness, corrosion resistance and structural stability at elevated temperatures. Hence, HEMs have great potential to be utilized in various high-tech areas, such as aerospace, high-temperature and nuclear energy fields, etc. HEMs have sparked great interests in the fields of materials and substantial progress has been made over the years. Powder metallurgy (PM) is an advanced technology that is often used to fabricate high-performance metal-based and ceramic composite materials possessing a metastable structure, such as nanocrystalline or supersaturated solid solution phases. In particular, it can also be applied to synthesize advanced materials with unique structures and properties that are difficult to achieve using conventional casting methods. Recently, PM has been extensively applied in studying HEMs, thereby considerably expanding their application range. In this review paper, we first introduce the concept and theories related to HEMs and briefly summarize research activities and progresses made with regards to the applications of PM in HEMs, including synthesis methods of powders, formation of bulk HEMs, and typical HEMs (i.e., nanocrystalline high-entropy alloys (HEAs), refractory HEAs, lightweight HEAs, dispersion strengthened HEAs, and high-entropy ceramics) fabricated using PM. In particular, we place emphasis on the mechanical properties and deformation behaviors of HEMs, specifically, the strengthening mechanisms in some typical HEAs fabricated by PM. Finally, the future prospects of HEMs are also briefly outlined.