Design of Light-Weight High-Entropy Alloys

Abstract

High-entropy alloys (HEAs) are a new class of solid-solution alloys that have attracted worldwide attention for their outstanding properties. Owing to the demand from transportation and defense industries, light-weight HEAs have also garnered widespread interest from scientists for use as potential structural materials. Great efforts have been made to study the phase-formation rules of HEAs to accelerate and refine the discovery process. In this paper, many proposed solid-solution phase-formation rules are assessed, based on a series of known and newly-designed light-weight HEAs. The results indicate that these empirical rules work for most compositions but also fail for several alloys. Light-weight HEAs often involve the additions of Al and/or Ti in great amounts, resulting in large negative enthalpies for forming solid-solution phases and/or intermetallic compounds. Accordingly, these empirical rules need to be modified with the new experimental data. In contrast, CALPHAD (acronym of the calculation of phase diagrams) method is demonstrated to be an effective approach to predict the phase formation in HEAs as a function of composition and temperature. Future perspectives on the design of light-weight HEAs are discussed in light of CALPHAD modeling and physical metallurgy principles.

Science and technology in high-entropy alloys

“…Thus, there are many corresponding calculation methods, the first-principles density functional theory (DFT), molecular dynamics (MD), discrete dislocation dynamics (DDD), phase-field method (PFM), thermodynamics model (TM), finite element method (FEM) [111], etc. For materials with different space scales, there are corresponding material calculation methods, including the calculation of phase diagram (CALPHAD) and high-throughput methods [26,65,69,[112][113][114][115][116][117].…”

“…Although the DFT has many simplifications of the Schrӧdinger equation, the computational process is still challenging due to the HEAs containing multiple principal components. Thus, hybrid Monte Carlo/molecular dynamics (MC/ MD) simulations, ab initio molecular dynamics (AIMD) simulations, special quasi-random structure (SQS) modeling, coherent potential approximation (CPA), even small sets of ordered structures (SSOS) calculations are used for the DFT calculation of HEAs [24,40,59,116,[129][130][131][132][133][134][135]. REVIEW .…”

“…However, if such data are not available unfortunately, it becomes necessary to design and carry out experiments. In this regard, the thermodynamic data obtained from the DFT calculations will be useful to fill up experimental data [31,116]. Thus, the reliable thermodynamic databases, containing a series of functions related to the composition and temperature, are assessed by the CALPHAD method, based on the reliable experimental data and accurate DFT results [40,50,[113][114][115][116][117][119][120][121][122].…”

Atomic and electronic basis for the serrations of refractory high-entropy alloys

“…5,9 Moreover, the formation of FCC-or BCC-type HEAs in a given multicomponent system can be estimated by the value of the VEC, i.e., VEC > 7.5~8 and VEC < 6~7.5 for FCC and BCC HEAs, respectively,. 5,9,11,17 Recently, a new approach has been established to accelerate the exploration of multicomponent alloys with solid-solution phases by combining calculated phase diagrams with simple rules based on the phases present, transformation temperatures, and attendant microstructures, 7 which introduces a technique to predict and achieve target properties (e.g., strength, modulus, and phase stabilities). 8,18,19 In the present work, we will describe and discuss the atomic and electronic foundations for the VEC-categorized and based principles in FCC or BCC HEAs.…”

TCHEA1: A Thermodynamic Database Not Limited for “High Entropy” Alloys

“…To meet the challenges, computational methods are indispensable. Different computational approaches, ranging from empirical rules [6,7] to semi-empirical CAL-PHAD method, [8][9][10][11][12] and to theoretical first principles method, [13,14] have been applied for screening of HEAs. For example, many empirical rules in terms of mixing enthalpy, configurational entropy, atomic size mismatch, valence electron concentration and their various combinations, have been proposed and tested to explore potential HEAs of simple solid solutions.…”