CALPHAD and rule-of-mixtures: A comparative study for refractory high entropy alloys

Present work studies 126 quaternary and 126 quinary equiatomic refractory high entropy alloys (RHEAs), made from Group IV (Ti, Zr, Hf), Group V (V, Nb, Ta) and Group VI (Cr, Mo, W) elements. Rule-of-mixtures (ROM) technique is used to calculate liquidus temperature, density (ρ), Young's modulus (E), % atomic size difference (δ), valence electron concentration (VEC) and specific heat at constant pressure and at 1273 K (Cp). CALPHAD technique is used to predict the number of phases formed at 298 K, ρ and liquidus temperature. ROM calculated densities are matching perfectly with CALPHAD values. Densities and E are directly proportional to the VEC and liquidus temperature of the alloys. Ti, Zr, Hf are ductilizing the alloys and making them light; whereas Cr, Mo and W, are reducing the alloys' ductility and making them heavy. For quinary RHEAs, Cp shows six distinct groups with δ, but a similar trend is not observed in quaternary RHEAs. A methodology is developed to screen a large number of alloys based on various properties. Correlations between those properties are also studied.