Design of non-equiatomic medium-entropy alloys

Abstract

High-entropy alloys have attracted much attention due to their unique microstructures and excellent properties. Since their invention more than ten years ago, research attention has been mainly focused on the study of multicomponent alloys with equiatomic or near-equiatomic compositions. Here we propose a novel design of non-equiatomic medium-entropy alloys that contain one matrix element and several equiatomic alloying elements. To verify the utility of this new design, a series of Co-free Fex(CrNiAl)100−x (at.%, 25 ≤ x ≤ 65) medium-entropy alloys were designed from the much-studied FeNiCrCoAl high-entropy alloy. Detailed characterization reveals that the alloys exhibit novel two-phase microstructures consisting of B2-ordered nanoprecipitates and BCC-disordered matrix. As the alloys deviate far from equiatomic composition, the structure of the nanoprecipitates transfers from a spinodal-like intertwined structure to a nanoparticle dispersed structure. Previous parametric approaches to predict phase formation rules for high-entropy alloys are unable to describe the phase separation behaviors in the studied alloys. Our findings provide a new route to design medium-entropy alloys and also demonstrate a strategy for designing nanostructured alloys from multicomponent alloy systems through simple variations in non-equiatomic compositions.

Influence of Cr Substitution and Temperature on Hierarchical Phase Decomposition in the AlCoFeNi High Entropy Alloy

“…The high resolution TEM results clearly show the coherency between the B2 and BCC phases. Such coherency has been observed in other alloys, e.g., the Fe 55 (CrNiAl) 45 alloys have two coherent phases, including the Ni-Al-rich B2 phase and the Fe-Cr-rich BCC phase 18 . Compositional analysis using TEM revealed more information about the composition of the phases.…”

Dynamic Mechanical Properties and Microstructure of an (Al0.5CoCrFeNi)0.95Mo0.025C0.025 High Entropy Alloy

“…For an n-element multicomponent alloy at a random state, the configurational entropy ΔS mix can be calculated according to Boltzmann’s hypothesis by the following equation [ 26 ]: where R is the gas constant and has a value of 8.314 JK −1 mol −1 , n is the number of total elements, and x i is the concentration of element i .…”

Investigation and Composition Characterization of a “NiTi-like” Alloy Combining High Temperature Shape Memory and High Entropy

“…In Fig. 1 of the work of Zhou et al [33], it is interesting to note that for a quinary alloy the compositions of the different elements will be between 5 at.% and 35 at.%. Several criteria are used in the metallurgy of high entropy alloys to increase the predictability of the single-phase solid solution formation.…”