High Entropy alloys

High entropy alloys (HEAs) are a new class of materials consisting of more than one principal element in a multi-component system. They are also known as multi-principal element alloys (MPEAs) or complex concentrated alloys (CCAs). The coupling of our CALPHAD based computational tools and databases allows a high fidelity calculation of thermodynamic properties and phase equilibria in multi-component HEAs, thus sheding light on the formation mechanism and thermodynamic and kinetic stability of HEAs, providing an efficient way to design HEAs for desired materials properties based on the prediction of microstructures through process optimisation.

Many research articles have been published using Thermo-Calc and our TCHEA database in the study of HEAs. The following are some application examples from these publications updated to 2017:

  • Precipitation behavior and its effects on tensile properties and the precipitation hardening of CoCrFeNi-based HEAs
  • Phase stability in the Al-Co-Cr-Fe-Mn-Ni subsystems
  • Thermodynamic instability of a nanocrystalline single-phase TiZrNbHfTa alloy and its impact on the mechanical properties
  • Phase transformation in the Al-Co-Cr-Cu-Fe-Ni system
  • Solid solubility in CoCrFeNiMx HEAs where M=4d transition metal
  • Design of MnFeNiCuCo HEA based on L10 structure
  • Long-term stability of HEAs in Al-Co-Cr-Cu-Fe-Mn-Ni subsystems
  • Materials design strategy on HEAs

In general, a vast amount of information can be obtained of relevance for HEAs by using our products.

Examples of equilibrium properties that can be predicted:

  • Phase amount and constitution as a function of composition
  • Phase amount and constitution as a function of temperature
  • Isopleth of a specific HEA system with varying compositions
  • Homogeneity range of HEAs
  • Thermo-stability of HEAs
  • Liquidus and solidus
  • Chemical orderings such as A2/B2, or A1/L12
  • Phase separations at low temperatures
  • Martensitic phase transformations
  • Partitioning of alloying elements among different phases
  • Entropy, enthalpy, heat capacity of phases or the system
  • Driving force for nucleation and growth e.g. of precipitates
  • Lattice parameter, density, thermal expansion and volume 

The solidification of HEAs during casting happens in a non-equilibrium way. The non-equilibrium solidification path can be predicted rather accurately by using the Scheil-Gulliver module available in Thermo-Calc. 

From a multicomponent Scheil-Gulliver calculation, one can obtain: 

  • Solidification temperature range
  • Incipient melting point
  • Phase amount and its composition
  • Phase formation sequence
  • Micro-segregation of solute elements
  • Latent heat evolution
  • Density variation and volume shrinkage 

By using the Diffusion Module (DICTRA) and combining TCHEA with compatible kinetic databases, typical diffusion-controlled phase transformations in HEAs can be simulated under arbitrary heat treatment conditions. 

Examples of applications that can be studied using the Diffusion Module (DICTRA) include: 

  • Growth or dissolution of intermetallic phases
  • Cooling effects in solidification
  • Homogenization of as-cast alloys
  • Coarsening of precipitate phases 

By using the Precipitation Module (TC-PRISMA) and combining thermodynamic and kinetic databases, the concurrent nucleation, growth and coarsening of precipitates can be simulated. 

Precipitation Module (TC-PRISMA) simulation results include the temporal evolution of: 

  • Mean radius
  • Number density
  • Volume fraction
  • Particle size distribution

Thermophysical Properties

The CALPHAD method has recently been extended to model additional thermophysical properties. The most recent version of the TCS High Entropy Alloys Database has viscosity of liquid and molar volume included. For more details see the link to the Technical Information PDF.