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Computation of stability, elasticity and thermodynamics in equiatomic AlCrFeNi medium-entropy alloys

Wen, Zhiqin, Zhao, Yuhong, Tian, Jinzhong, Wang, Shuo, Guo, Qingwei, Hou, Hua
Journal of materials science 2019 v.54 no.3 pp. 2566-2576
alloys, crystal structure, entropy, heat, magnetism, models, modulus of elasticity, solid solutions, temperature, thermal expansion
We investigated the phase stability, elastic and thermodynamic properties of equimolar medium-entropy alloys (MEAs) AlCrFeNi by performing first-principles calculations in combination with quasi-harmonic Debye–Grüneisen model. Both body-centered cubic (BCC) and face-centered cubic structures in ferromagnetic (FM) and non-magnetic states are described using the special quasirandom structures technique. All the considered MEAs can form single-phase solid solutions and are dynamically stable, and FM BCC AlCrFeNi is the most stable. The elastic moduli including bulk modulus B, shear modulus G and Young’s modulus E of AlCrFeNi are calculated by first-principles and estimated by using the rule of mixtures (ROM) from their pure components. The lattice constants a of first-principles calculations are well reproduced by ROM. The obtained B and G of the two methods are close to equality lines with a minor scatter. The relevant free energies’ contributions including structural, configurational, vibrational and electronic excitations are taken into account to calculate the equilibrium lattice constants a, volumetric thermal expansion coefficient α, Debye temperature ΘD, constant volume heat capacity Cᵥ, vibrational entropy Sᵥᵢb, electronic entropy Sₑₗₑc, vibrational Helmholtz free energies Fᵥᵢb and electronic Helmholtz free energies Fₑₗₑc of AlCrFeNi MEAs at finite temperature. The thermodynamic properties strongly depend on crystal structures and magnetic states, and FM BCC AlCrFeNi shows the largest Sᵥᵢb and α, and the lowest Fᵥᵢb among the considered MEAs. Finally, electronic density of states is analyzed to clarify the physical origin of AlCrFeNi MEAs with different crystal structures and magnetic states.