Phase stability and microstructures of high entropy alloys ion irradiated to high doses

Abstract

The microstructures of Al x CoCrFeNi (x = 0.1, 0.75 and 1.5 in molar ratio) high entropy alloys (HEAs) irradiated at room temperature with 3 MeV Au ions at the highest fluence of 105, 91, and 81 displacement per atom, respectively, were studied. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) analyses show that the initial microstructures and phase composition of all three alloys are retained after ion irradiation and no phase decomposition is observed.Furthermore, it is demonstrated that the disordered face-centered cubic (FCC) and disordered body-centered cubic (BCC) phases show much less defect cluster formation and structural damage than the NiAl-type ordered B2 phase. This effect is explained by higher entropy of mixing, higher defect formation/migration energies, substantially lower thermal conductivity, and higher atomic level stress in the disordered phases. © 2016. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ 2 / 37 efficient and economical and produce less radioactive waste [4], the high-performance structural materials will be required to withstand severer environment, such as higher temperatures and irradiation doses, which exceeds the limits of current nuclear materials. Therefore, the advanced nuclear reactor designs call for dramatic progress in materials, and numerous new materials, such as oxide dispersion steel (ODS) [5], bulk metallic glass (BMG) [6], ceramic materials [7], and bulk nano-layered (NL) composites [8], have been investigated in order to be used in the advanced nuclear reactors [9].Recently, high entropy alloys (HEAs) [10][11][12][13][14][15][16], which are based on the concept of concentrated multi-component solid solution, have shown attractive properties in mitigating irradiation damages, e.g., in CoCrCuFeNi HEA [17], Al x CoCrFeNi HEAs [18,19], and refractory HfNbZr medium-entropy alloy [20,21]. The FCC structure of the as-sputtered CoCrCuFeNi remained stable against irradiation over a wide temperature range from 298 K to 773 K without inducing grain coarsening [17]. The preliminary results by Xia et al. [18,19] showed that the Al x CoCrFeNi alloys exhibited excellent structural stability up to over 50 displacement per atom (dpa) at 298 K, and that the irradiation-induced volume swelling of the FCC solid solution is lower than BCC solid solution, which is in contrast to traditional materials for which the swelling volume in the FCC structure is generally larger than the BCC structure [22]. However, the underlying mechanisms were not understood. Therefore, this study aims to provide more in-depth and thorough TEM and HRTEM studies of their microstructures before and after irradiation, and attempts to rationalize their extraordinary irradiation resistance from the perspectives of lattice phonon vibration, thermal conductivity, and diffusion, and atomic stresses.

Science and technology in high-entropy alloys

“…These outstanding properties make it possible for the HEAs to be used in turbine blades of aircraft [79], and cryogenic environments [36] as engineering alloys. HEAs possess low swelling after ion irradiation and some selfhealing effects that has good application prospect in the field of nuclear materials [142].…”

Single-Phase Concentrated Solid-Solution Alloys: Bridging Intrinsic Transport Properties and Irradiation Resistance

“…The phase stability of FCC SP-CSAs at room temperature has been examined in both NiCoFeCr (Abhaya et al, 2016) and NiCoFeCrAl 0.1 (Xia et al, 2016) under high dose irradiations up to ∼100 dpa. No observable secondary phase was observed in both studies.…”

Configurational Entropy in Multicomponent Alloys: Matrix Formulation from Ab Initio Based Hamiltonian and Application to the FCC Cr-Fe-Mn-Ni System

“…At or near equiatomic ratio of compositions, the configuration entropy is maximized and given by the formula S con f ig /R = lnK where R is the ideal gas constant, and K is the total number of different components. It has been proposed to define K = 4 as the minimum number of components at or near equiatomic composition for these systems to be called HEAs [3][4][5].…”