An assessment on the future development of high-entropy alloys: Summary from a recent workshop

Abstract

a b s t r a c tThere is increasing interest in both relating the mechanical behavior of high-entropy alloys to their microstructural evolution and in their development for various applications. A special two-day international workshop on the above topic was held in Guiyang, China, in December 2014. The workshop gathered scientists and engineers to exchange information on recent progress in high-entropy alloys, to discuss the scientific issues and challenges to foster international collaborations, and to identify future directions. In this paper, a summary of this workshop is presented, including aspects of definition/terminology, phase formation, microstructure and phase stability, strengthening mechanisms, and hightemperature properties. Future research directions are also outlined. SynopsisThe continued development of high-performance materials is required for increased energy efficiency and sustainability. Traditionally, metallic alloys have been widely applied as structural materials. The conventional alloy design strategy usually is to start with one element as the principal constituent and adding other minor elements for the further optimization of properties and performances. After extensive efforts on these traditional alloys, the development of traditional alloys is approaching its limits. Recently, a new alloy design concept was proposed: the idea is to simultaneously alloy several principal elements (usually !5) to obtain high mixing entropy. As a result, many novel concentrated multicomponent alloys are in the process of being developed [1e6]. In a timely response to this rapid development, a two-day international workshop was held in Guiyang, PRC in December 2014 to exchange information on recent progress, foster international collaborations, and identify future research directions. The main theme of the workshop was the relationship between microstructures and mechanical properties. In this paper, a summary of this special workshop is presented, which includes; 1) Definition/terminology, 2) Main characteristics resulting from multiple primary constituents, 3) Atomic size effects on phase formation, 4) Microstructure and phase stability, 5) Strengthening mechanisms, 6) High-temperature mechanical properties, and 7) Future directions for research Definitions/terminologyAlthough "high-entropy alloys (HEAs)" have now become a new class of materials, the name has not been clearly defined since its inception. This often causes confusion in the scientific community.

Crystallographically degenerate B2 precipitation in a plastically deformed fcc-based complex concentrated alloy

“…In recent years, studies have shown that phase formation in a large variety of CCAs is driven by enthalpy considerations; rather than entropy [1,2]. Under the circumstances, several alloy compositions are susceptible to secondary phase formation, thus allowing the design of precipitation-hardenable CCA compositions [3][4][5][6]. In most cases the strengthening precipitate nucleates homogeneously within the parent matrix, where nucleation involves a complex interplay among chemical, elastic (due to misfit strains) and interfacial energies [7,8].…”

Alloy design for intrinsically ductile refractory high-entropy alloys

“…The recently emerging high-entropy alloys (HEAs), however, provide a novel alloying strategy that significantly expands the scope of the conventional alloy design. [3][4][5][6][7][8][9][10][11][12] HEAs typically consist of at least four principal metallic elements in near-equiatomic ratios and therefore have a higher configuration entropy than that in conventional alloys. Due to their unique features, including high softening resistance at elevated temperatures, the slow diffusion kinetics, and high oxidation resistance, HEAs naturally possess the advantages to be considered as new types of high-temperature alloys.…”

Deformation Behavior of Al0.25CoCrFeNi High-Entropy Alloy after Recrystallization

“…Attributed to the high mixing configurational entropy, HEAs always remain as stable crystal structures, such as body-centered cubic (BCC) [3], face-centered cubic (FCC) [4,5], or hexagonal close-packed (HCP) [6], rather than complex intermetallic phases [5,7,8]. The definition and rules governing the phase formation in HEAs are a matter of great interest and debate at present [9,10]. However, the structure of HEA solid solutions are significantly different from those of Hume-Rothery terminal solid solutions, and this offers many potential applications, including tools, molds, and mechanical parts [11].…”