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APPLICATIONS OF THERMO-CALC

High Entropy Alloys

Thermo-Calc can be used to predict thermophysical and phase-based properties as well as to simulate material behavior over the wide range of possible alloy compositions in the HEA space to accelerate alloy design.

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Applications for High Entropy Alloys

High entropy alloys (HEAs) are a new class of materials consisting of more than one principal element in a multicomponent system. They are also known as multi-principal element alloys (MPEAs) or complex concentrated alloys (CCAs). This is an area of fast-paced research where there are as yet no well-established commercial alloys. As such, handbook data is lacking for this class of materials, and additionally, is unsuited to new alloy discovery and design.

Thermo-Calc can be used to calculate materials property data systematically to explore a range of compositions and make predictions of material behavior throughout the materials life cycle.

Calculate the following based on your actual alloy chemistry:

  • Thermophysical properties, such as:
    • Specific heat, enthalpy, latent heat, viscosity, density as a function of temperature, coefficients of thermal expansion, and more
    • Phase-based properties, such as:
      • Critical transformation temperatures such as solvus temperatures of precipitates, amounts and compositions of phases, solubility limits, activities, phase diagrams, and more
        • Determine compositions that lead to single phase
        • Elastic properties:
          • Elastic moduli (bulk modulus, shear modulus, and Young’s modulus) for BCC, HCP, and FCC phases
            • Elastic constants (C11, C12, C13, C33, and C44) for BCC, HCP, and FCC phases
            • Equilibrium and non-equilibrium solidification, such as:
              • Liquidus, solidus, incipient melt temperatures, freezing range, fraction solid curves, solidification path, fraction eutectic, microsegregation, partition coefficients, latent heat, shrinkage, and more
              • Homogenization/Solutionizing:
                • Optimal homogenization temperatures, time needed to homogenize any chemical segregation arising from solidification, and/or dissolve precipitates
                • Aging/Precipitation hardening:
                  • Concurrent nucleation, growth/dissolution, coarsening of precipitate phases, volume fraction, and size distribution as a function of time

Application Examples

Thermo-Calc has many applications to high entropy alloys. Below are two such examples.

Calculate Multicomponent Phase Diagrams

CoCrFeNi is one of the most studied HEA alloys. It has a narrow solidification temperature range and is single phase disordered FCC_A1 across a wide temperature range. An ordered precipitate phase could increase its high temperature strength. Thermo-Calc can be used to explore chemistry ranges and modifications to tailor phase balance for optimum properties.

This phase diagram for CoCrFeNi-Alx shows how additions of Al change the phase stability. At higher amounts of Al, ordered BCC_B2 phase is predicted to be stable. At even higher Al contents, the matrix phase switches to a BCC_A2 disordered phase.

A plot of an CoCrFeNi-Alx Isoplethal phase diagram.

Calculating Stability Diagram for Undesirable Precipitates

A Heusler phase with an incoherent L21 structure can be detrimental in FCC strengthened HEAs where the main strengthening precipitate is expected to be a coherent γ’ (L12 structure) type precipitate. Thus, for chemically complex HEAs, the amount of Ni, Al, and Ti drives the precipitation behavior of the material. It is, therefore, useful to use phase stability diagrams to look at composition-temperature ranges wherein such undesirable phases are present and minimize them.

Based on work from [Zhang, 2022], the figure shows an isopleth of (FeCoCr)90-xNixTi2Al8 (at%) showing the engineering composition-temperature range for FCC HEAs with precipitation-strengthening attributes to Heusler and other ordered phases such as γ’-L12 at low temperatures. The plot was produced using the High Entropy Alloys Database (TCHEA).

A plot of an isopleth of (FeCoCr)90-xNixTi2Al8 (at%) showing the engineering composition-temperature range for FCC HEAs with precipitation-strengthening attributes to Heusler and other ordered phases such as γ’-L12 at low temperatures.
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Learn more about Applications to High Entropy Alloys

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Navigating the BCC-B2 refractory alloy space: Stability and thermal processing with Ru-B2 precipitates

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Using CALPHAD-based Tools for the Study and Design of High Entropy Alloys

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Mixing Entropy of Exact Equiatomic High-Entropy Alloys Formed into a Single Phase

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Solid Solutions with bcc, hcp, and fcc Structures Formed in a Composition Line in Multicomponent Ir–Rh–Ru–W–Mo System

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Presentation on High Entropy Alloys Database Development

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