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The present is a novel, systematic study of the effect of density functional theory input parameters on the vacancy formation energy (VFE), migration barrier for diffusion, and electronic structure for each element in the CoCrNi medium-entropy alloy (MEA). In particular, the novelties include: (1) calculating the aforementioned properties of Co, Cr, or Ni, in the CoCrNi MEA using magnetic and non-magnetic states, and two versions of the generalized gradient approximation: Perdew, Burke, and Ernzerhof (PBE) and the PBE version for solids (PBEsol), and (2) a detailed comparison of 0 K activation energy to experimental creep activation energies. First-principles calculations at 0 K are performed using the Vienna ab-initio simulation package. Special quasirandom structures (SQS) and Widom-type substitution are employed. For each element, Co, Cr, or Ni, non-magnetic calculations result in a higher VFE and larger range of calculated values for the configurations studied. The averaged migration barrier is the highest for Co in the CoCrNi for three of four sets of calculation parameters in the configurations studied. Finally, the results indicate that the average 0 K activation energy for diffusion makes up 70–80% of the experimental creep activation energy, depending on the exchange-correlation functional employed. • For each element, Co, Cr, and Ni in CoCrNi, non-magnetic calculations produced a higher VFE than the corresponding magnetic calculations. The non-magnetic calculations also produced the widest range of VFE values. • The calculated VFE of Cr and Ni in the CoCrNi are higher than the corresponding pure element VFE reported in the literature regardless of which calculation settings are employed. • For three of the four sets of calculation parameters, the averaged vacancy migration barrier is the highest for Co in the CoCrNi and the lowest for Cr in the CoCrNi. • When used as a baseline, the 0 K activation energy averaged for Co, Cr, and Ni makes up 75–80% of the experimentally reported creep activation energy in this CoCrNi MEA, depending on which exchange-correlation functional is used for the calculations.
Lafferty et al. (Thu,) studied this question.