The Different Roles of Entropy and Solubility in High Entropy Alloy Stability

Abstract

Multiprincipal element high entropy alloys stabilized as a single alloy phase represent a new material system with promising properties, such as high corrosion and creep resistance, sluggish diffusion, and high temperature tensile strength. However, the mechanism of stabilization to form single phase alloys is controversial. Early studies hypothesized that a large entropy of mixing was responsible for stabilizing the single phase; more recent work has proposed that the single-phase solid solution is the result of mutual solubility of the principal elements. Here, we demonstrate the first self-consistent study of the relative importance of these two proposed mechanisms. In situ high-throughput synchrotron diffraction studies were used to monitor the stability of the single phase alloy in thin-film (Al1-x-yCuxMoy)FeNiTiVZr composition spread samples. Our results indicate that a metastable solid solution can be captured via the rapid quenching typical of physical vapor deposition processes, but upon annealing the solid-solution phase stability is primarily governed by mutual miscibility.

Powder Metallurgy Processing of a WxTaTiVCr High-Entropy Alloy and Its Derivative Alloys for Fusion Material Applications

“…The diffraction peaks of the samples sintered at 40°, 58° and 73° from the (110), (200), and (211) planes, respectively, confirm the presence of a BCC crystal structure, as observed previously in sintered refractory alloys 53 and HEAs 103, 133 due to the high degree of mutual solubility of their constituents 134, 135 . The presence of intermetallics in HEAs is well known 89, 93 ; however, the low volume fraction of intermetallics prevents XRD patterns from giving any indication of their presence.…”

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

“…If there were more elements with a major concentration, no matrix element can be identified. It was generally accepted in physical metallurgy that increasing the number of elements in an alloy most likely favors the formation of intermetallic phases and complex microstructures or even promotes the freezing of amorphous liquids, yielding eventually metallic glasses [2,3]. Multi-component equiatomic solid solutions as, e.g., the Cantor alloy, do not fall into these categories.…”

“…Thus, high entropy alloys are defined as solid solutions with at least five elements whose individual concentrations may range between 5 and 35 at.%. However, present views on this new material class have shown that the large configurational entropy is neither sufficient nor necessary to form multi-component solid solutions [3,[5][6][7], but the name of the family was established.…”

Thermodynamic Routes to Ultralow Thermal Conductivity and High Thermoelectric Performance

“…Note that the formation energies of native and extrinsic defects are temperature dependent, affording a new control parameter for performance optimization. In addition, the high configurational entropy effect tends to extend the solubility limit of specific elements 62,63. When the nominal composition crosses the phase boundary, a secondary phase is formed.…”