Vacancy Energetics and Diffusivities in the Equiatomic Multielement Nb-Mo-Ta-W Alloy

Area of Science:

• Materials Science
• Computational Materials Science
• Physical Metallurgy

Background:

• High-entropy alloys like Nb-Mo-Ta-W are crucial for advanced applications.
• Understanding defect behavior, particularly vacancies, is key to predicting alloy performance.
• Short-range order (SRO) and dislocations significantly influence material properties.

Purpose of the Study:

• To investigate vacancy formation and migration energies in equiatomic Nb-Mo-Ta-W alloys.
• To analyze the impact of SRO and edge dislocation cores on vacancy energetics.
• To determine the effect of energy distribution asymmetry on vacancy diffusivity.

Main Methods:

• Molecular statics calculations utilizing a specialized spectral neighbor analysis potential.
• Metropolis Monte Carlo relaxations to incorporate SRO and temperature effects.
• Nudged elastic band (NEB) method for calculating vacancy migration energies.

Main Results:

• Vacancy formation and migration energies exhibit a wide statistical distribution (up to 1.0 eV).
• Significant dependence of vacancy energetics on SRO and proximity to edge dislocation cores.
• Hypothesized formation of stable 'superjogs' due to low-energy vacancy formation at dislocation cores.
• Asymmetric thermal sampling leads to effective vacancy formation energies lower than averages.

Conclusions:

• Vacancy energetics in Nb-Mo-Ta-W alloys are complex and highly sensitive to local atomic arrangements.
• The observed phenomena significantly influence vacancy diffusivity and overall alloy structural behavior.
• Findings provide critical insights for designing and optimizing refractory high-entropy alloys.