Abstract
We present detailed comparisons between the results of embedded atom model (EAM) and density functional theory (DFT) calculations on defected Ni alloy systems. We find that the EAM interatomic potentials reproduce low-temperature structural properties in both the γ and phases, and yield accurate atomic forces in bulk-like configurations even at temperatures as high as ∼1200 K. However, they fail to describe more complex chemical bonding, in configurations including defects such as vacancies or dislocations, for which we observe significant deviations between the EAM and DFT forces, suggesting that derived properties such as (free) energy barriers to vacancy migration and dislocation glide may also be inaccurate. Testing against full DFT calculations further reveals that these deviations have a local character, and are typically severe only up to the first or second neighbours of the defect. This suggests that a QM/MM approach can be used to accurately reproduce QM observables, fully exploiting the EAM potential efficiency in the MM zone. This approach could be easily extended to ternary systems for which developing a reliable and fully transferable EAM parameterisation would be extremely challenging e.g. Ni alloy model systems with a W or Re-containing QM zone.
Highlights
Ni-based superalloys are high performance structural materials that exhibit excellent strength and creep resistance at high temperatures, even in chemically aggressive environments [1, 2]
Our goal is to investigate the accuracy of the embedded atom model (EAM) potential by comparing the atomic forces it produces with those obtained from density functional theory (DFT) calculations
We have presented detailed comparisons between the result of embedded atom model and density functional theory-based approaches to modelling defect systems in Ni and Ni3Al (γ /γ′) systems
Summary
Ni-based superalloys are high performance structural materials that exhibit excellent strength and creep resistance at high temperatures, even in chemically aggressive environments [1, 2] They are manufactured in polycrystalline form for turbine disks and in single crystal form for turbine airfoils. Non-uniform precision techniques such as the ‘learn on the fly’ (LOTF) multiscale quantum mechanical/molecular mechanical (QM/MM) scheme [16, 17] appear promising, they have not yet been extensively applied to metallic systems [18,19,20] Augmenting this approach by learning algorithms that allow performing QM calcul ations only where and when they are necessary could further reduce the overall computational cost [21].
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