Breakthrough applications of high-entropy materials
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ARTICLE Breakthrough applications of high-entropy materials Jien-Wei Yeha) and Su-Jien Lin Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan, Republic of China (Received 17 April 2018; accepted 25 July 2018)
The concept of high-entropy alloys has been extended to ceramics, polymers, and composites. “High-entropy materials (HEMs)” are named to cover all these materials. Recently, HEMs has become a new emerging field through the collective efforts of many researchers. Basically, high mixing entropy can enhance the formation of solution-type phases for alloys, ceramics, and composites at high temperatures, and in general leads to simpler microstructure. Large degrees of freedom in composition design as well as process design have been found to provide a wide range of microstructure and properties for applications. There are many opportunities for HEMs to overcome the bottlenecks of conventional materials. In this article, several possible breakthrough applications are pointed out and emphasized for turbine blades, thermal spray bond coatings, high-temperature molds and dies, sintered carbides for cutting tools, hard coatings for cutting tools, hardfacings, and radiation-damage resistant materials. In addition, more possible breakthrough examples are briefly described.
I. INTRODUCTION
High-entropy alloys (HEAs) have been developed in late 20th century but formally published in the early 21st century.1,2 Two definitions of HEAs were proposed based on composition and configurational entropy, respectively. For compositional definition,3 HEAs are preferentially defined as alloys containing at least five principal elements, each with an at.% between 5 and 35%. The at.% of each minor element, if any, is hence less than 5%. For the entropic definition,4 HEAs are defined as alloys having configurational entropies at a random state larger than 1.5R, no matter they are single phase or multiphase at room temperature. From the concept of HEAs, the alloy world can be divided as three categories based on configuration entropy: HEAs are those with configurational entropy larger than 1.5R, where R is gas constant; medium-entropy alloys (MEAs) between 1 and 1.5R; and low-entropy alloys smaller than 1R. Furthermore, an extension of HEA concept was soon carried out to ceramics (HECs), polymers (HEPs), and composites (HECOMPs) by changing the at.% in compositional definition into the mole percentage. As for HECOMPs, at least one of the main components should be of HEAs, HECs, or HEPs. As a result, materials world can also be divided into high-entropy, medium-entropy, and lowentropy materials to cover all possible materials. Since conventional materials consist of one or two major components whereas medium-entropy materials (MEMs) a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2018.283 J. Mater. Res., 2018
and high-entropy materials (HEMs) have more major elements or components, the whole periodic table could become fully activated in the materials des
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