High-Entropy Alloys: Overview

As it is a normal way for mankind to develop alloys from simple to complex compositions, it might be expected that some ancient metallurgists had tried to make alloys in high concentrations of various existing metal elements. This development might increase the variety of alloys for different applications. However, all these attempts would be hindered by the fact that their tried compositions were not easily mixed together by existent technique or became too brittle even after fabrication to a form. Even modern metallurgy or materials science also teach that it is not plausible to design multi-principal-element compositions since many brittle intermetallic compounds would be involved in the microstructure and make the materials useless. However, the unbreakable misconception has been broken by Jien-Wei Yeh and Brian Cantor, both independently announced high-entropy alloys and equi-atomic multi-component alloys, respectively in their reports published in 2004, the beginning of 21th century. Now, we realize that high entropy effect is the most important factor to enhance the mixing and formation of solid solution phases which can simplify the microstructures and improve the ductility and other properties as long as compositions are suitably designed. This breakthrough in alloy composition concept has evoked the scientists and engineers to notice the unknown composition field. There showed an abrupt jump in the number of papers on high-entropy alloys after 8-years steady growth, i.e., since 2013. We are expecting the new life of the periodic table in generating new materials world. In this article, we will describe the development history from conventional composition to multi-principal-element compositions, the future trends and prospects.