1 High entropy effect and high entropy alloy
The concept of high entropy effect comes from the high entropy alloy, and the concept of high entropy alloys is first proposed and confirmed by two research groups of China’s National Tsinghua University and University of Bradford. So far, it has undergone 15 years of development. From the Cu, Co, Ni, Cr, Al, Fe and V metals, at least 5 alloy elements were selected and mixed according to the near mole ratio, using sputtering, melting, and so on. Alloys or alloy coatings prepared by casting have simple single-phase face centered cubic (FCC) or body centered cubic (BCC) crystal structure and extraordinary mechanical properties, and have phase stability that conventional metals do not have. This alloy is defined as high entropy alloy, which opens the prelude to the research of high entropy alloy.
2 Characteristics of high entropy effect
3 Research status of high entropy ceramics
In 2015, Rost, Maria and curtarolo reported a high entropy ceramic material for the first time. They took MgO, NiO, COO, CuO and ZnO as the initial raw materials. In addition to CuO and ZnO, the other three oxides are rock salt ore structure. Single phase (mgnicocuzn) O high entropy ceramics can be formed by uniformly mixing five oxides, heating in air and holding at 875 ℃ for 12h.
(2) High entropy boride ceramics
The research of high entropy boride ceramics mainly focuses on transition metal IVB and diboride (MB2) of VB group. Most of these borides have AlB2 hexagonal structure, that is, B atoms form a layered structure similar to graphite, and metal atoms are interspersed between layers. It is precisely because of the strong covalent characteristics of B-B ring and M-B bond that MB2 has high melting point, hardness, strength, thermal stability and conductivity, so it can be used in armor materials, aviation materials Cutting tools, materials and other fields. The high entropy theory brings more space to the design of new boride ceramics. Through the design of different components, a variety of multicomponent solid solutions can be formed, which greatly expands the types of ultra-high temperature ceramics, and can more finely regulate their properties.
(3) High entropy carbide ceramics
At present, the research of high entropy carbide ceramics mainly focuses on the solid solution of transition metal IVB and VB carbides. These carbides have rock salt structure and, like borides, have strong covalent bond characteristics and high melting point, which can be applied to various extreme conditions. The solid solution of multiple metal ions into one crystal also greatly expands the types of carbide ceramics.
The research on transition group refractory metal carbide high entropy ceramics initially focused on five component (tizrhfnbta) C high entropy ceramics, and gradually expanded to (tizrhfvnb) C, (tizrnbtamo) C, (tizrnbtaw) C and (tihfvnbta) C. However, there are also reports on three component carbide solid solution ceramics (zrnbta) C, (zrnbti) C and four component carbide solid solution ceramics (hftazrti) C, (hftazrnb) C and (zrnbtiv) C. At the same time, in order to maximize the mixing entropy, the content of each component in the reported carbide high entropy ceramic system is equal molar ratio.
(4) Other non oxide high entropy ceramics
In addition to the above common oxides, borides and carbides, high entropy nitrides, silicides and thermoelectric materials have also been reported. Among them, nitride is one of the first reported high entropy materials.
Reference source:
Wang Xiaopeng et al New progress in high entropy alloys and other high entropy materials Harbin Institute of Technology
Chen Lei et al Research progress of transition metal non oxide high entropy ceramics Harbin Institute of Technology
Gu Junfeng et al Research progress of high entropy ceramic materials Wuhan University of Technology