Exploration and Development of High Entropy Alloys for Structural Applications

Abstract

Abstract:We develop a strategy to design and evaluate high-entropy alloys (HEAs) for structural use in the transportation and energy industries. We give HEA goal properties for low (≤150 °C), medium (≤450 °C) and high (≥1,100 °C) use temperatures. A systematic design approach uses palettes of elements chosen to meet target properties of each HEA family and gives methods to build HEAs from these palettes. We show that intermetallic phases are consistent with HEA definitions, and the strategy developed here includes both single-phase, solid solution HEAs and HEAs with intentional addition of a 2nd phase for particulate hardening. A thermodynamic estimate of the effectiveness of configurational entropy to suppress or delay compound formation is given. A 3-stage approach is given to systematically screen and evaluate a vast number of HEAs by integrating high-throughput computations and experiments. CALPHAD methods are used to predict phase equilibria, and high-throughput experiments on materials libraries with controlled composition and microstructure gradients are suggested. Much of this evaluation can be done now, but key components (materials libraries with microstructure gradients and high-throughput tensile testing) are currently missing. Suggestions for future HEA efforts are given.

Understanding the physical metallurgy of the CoCrFeMnNi high-entropy alloy: an atomistic simulation study

“…1 Particularly, the equiatomic CoCrFeMnNi HEAs have been reported to possess a wide-range of promising properties such as good hightemperature structural stability 2,3 and an excellent balance between strength and ductility, particularly at cryogenic temperatures, typically 77 K, the liquid nitrogen temperature. 4 Even though most HEAs have equiatomic or near equiatomic compositions, it is believed that the equiatomic composition would not be the optimum composition for a wide range of material properties.…”

Predicting the formation and stability of single phase high-entropy alloys

“…This combinatorial algorithm is described in detail, and its software implementation is freely accessible through a webservice allowing rapid advances in the design, development and discovery of new technologically important alloys. , and re-iterated by others since then [1,12], defines a HEA as any alloy consisting of 5 or more elements between 5 -35 at. %.…”

Influence of Annealing on the Microstructures and Oxidation Behaviors of Al8(CoCrFeNi)92, Al15(CoCrFeNi)85, and Al30(CoCrFeNi)70 High-Entropy Alloys

“…In contrast to conventional alloys, HEAs lack a primary constituent and are generally composed of five or more elements in nearly equal proportions [1,2]. It is well-known that these alloys typically form phases with simple FCC, BCC, and HCP crystal structures and can contain ordered intermetallic phases [4].…”

“…Recently, a novel class of compositionally-complex alloys termed high-entropy alloys (HEAs) have attracted substantial interest in the scientific community [1][2][3][4]. In contrast to conventional alloys, HEAs lack a primary constituent and are generally composed of five or more elements in nearly equal proportions [1,2].…”

“…This particular alloy system is ideal for a fundamental oxidation study since it contains both Al and Cr, which are known to produce protective Cr 2 O 3 and/or Al 2 O 3 scales [30]. Additionally, the AlCoCrFeNi system is one of the most thoroughly investigated to date [1,4,10,14,[31][32][33][34][35][36][37][38][39][40][41][42][43]. This paper will systematically report the influence of annealing on the microstructures and active oxidation mechanisms.…”