Thermodynamic modelling to predict phase stability in BCC + B2 Al–Ti–Co–Ni–Fe–Cr high entropy alloys

• This paper examines the potential of thermodynamic modelling as a simple and inexpensive means for assessing phase stability in a series of non-equiatomic high entropy alloys and compares with CALPHAD calculations to demonstrate an appropriate level of simplifying assumptions. The modelling was motivated by alloys from the Al–Ti–Co–Ni–Fe–Cr system, which were produced by iteratively following the natural compositional segregation of the two-phase BCC + B2 microstructure present in a Al2TiCoNiFeCr alloy after casting and heat treatment. This produced a range of multicomponent B2-type alloys with different volume fractions of a BCC secondary phase. The solubility limits and traditional empirical thermodynamic driving forces for phase stability were investigated to explain the formation of the two phases. Limitations of prior semi-empirical models are highlighted, with advancements demonstrated by accounting for contributions from the effect of ordering on configurational entropy, the difference in enthalpy from intermetallic compounds, and thermal influences on both entropy and enthalpy. The new models are compared against the current leading thermodynamic modelling approach, CALPHAD, with excellent correlation. This work outlines a methodology to predict and design phase constitution in future high-performance BCC + B2 alloys and, more generally, it demonstrates the value of models with temperature-dependent thermodynamic quantities for exploring new, complex compositional regions.

Subject headings

TEKNIK OCH TEKNOLOGIER  -- Materialteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering (hsv//eng)

Keyword

B2 crystal structure

BCC crystal Structure

CALPHAD

High entropy alloys

Thermodynamic stability

Aluminum alloys

Chromium alloys

Cobalt alloys

Enthalpy

Entropy

High-entropy alloys

Iterative methods

Phase stability

Titanium alloys

B2 crystal

Crystals structures

Simple+

Thermodynamic modelling

Two phase

Crystal structure

Publication and Content Type

ref (subject category)

art (subject category)