Single-phase high-entropy alloys – an overview

Abstract

Abstract:The term "high-entropy alloys (HEAs)" first appeared about 10 years ago defining alloys composed of n = 5-13 principal elements with concentrations of approximately 100/n at.% each. Since then many equiatomic (or near equiatomic) single-and multi-phase multicomponent alloys were developed, which are reported for a combination of tunable properties: high hardness, strength and ductility, oxidation and wear resistance, magnetism, etc. In our paper, we focus on probably single-phase HEAs (solid solutions) out of all HEAs studied so far, discuss ways of their prediction, mechanical properties. In contrast to classical multielement/multiphase alloys, only single-phase multielement alloys (solid solutions) represent the basic concept underlying HEAs as mixing-entropy stabilized homogenous materials. The literature overview is complemented by own studies demonstrating that the alloys CrFeCoNi, CrFeCoNiAl 0.3 and PdFeCoNi homogenized at 1300 and 1100°C, respectively, for 1 week are not singlephase HEAs, but a coherent mixture of two solid solutions.

Structure of some CoCrFeNi and CoCrFeNiPd multicomponent HEA alloys by diffraction techniques

“…Recently by TEM investigations on CCFN samples that were homogenized at 1300°C (about 120 degrees below the melting point) for 1 week an onset of phase decomposition was detected [6].…”

“…Multicomponent metallic alloys of the type usually called High Entropy Alloys (HEAs) have recently raised considerable attention because of their attractive physical properties [1][2][3][4][5][6] such as high hardness, outstanding wear resistance, good high-temperature strength and thermal stability.…”

“…It has been extensively studied during the last ten years and has been reported to be single-phase and a true solid solution [6,13,[32][33][34]. However, recently it was reported that CCFN alloys homogenized for a long time at high temperature are not single-phase but a coherent mixture of two solid solutions [6].…”

“…It has been extensively studied during the last ten years and has been reported to be single-phase and a true solid solution [6,13,[32][33][34]. However, recently it was reported that CCFN alloys homogenized for a long time at high temperature are not single-phase but a coherent mixture of two solid solutions [6]. This conforms to the present study as well as to the earlier findings in [9,35,36] where composition fluctuations as well as fluctuations in the lattice constants as a function of position were reported in an as-cast CCFN ingot produced by arc melting and subsequent casting.…”

Face Centred Cubic Multi-Component Equiatomic Solid Solutions in the Au-Cu-Ni-Pd-Pt System

“…Presently, there are only a few truly single-phase high entropy alloys known [8], i.e., CoCrFeMnNi (fcc) [1], AlLiMgScTi (fcc) [9], AlCoCrFeNi (bcc) [10], HfNbTaTiZr (bcc) [11], MoNbTaVW (bcc) [12] and DyGdHoTbY (hcp) [13]. The latter three are noteworthy, since the solid solution is observed within the complete concentration range for the known binary and ternary systems formed upon these elements.…”