Ab Initio Modeling of Bulk and Intragranular Diffusion in Ni Alloys.
Knowledge of solid-state and interfacial species diffusion kinetics is of paramount importance for understanding mechanisms of grain boundary (GB) oxidation causing environmental degradation and cracking of Ni-base structural alloys. In this study, first-principles calculations of vacancy-mediated diffusion are performed across a wide series of alloying elements commonly used in Ni-based superalloys, as well as interstitial diffusion of atomic oxygen and sulfur in the bulk, at the (111) surface, ⟨110⟩ symmetric tilt GBs of Ni corresponding to model low- (Σ = 3/(111)) and high-energy (Σ = 9/(221)) GBs. A substantial enhancement of diffusion is found for all species at the high-energy GB as compared with the bulk and the low-energy GB, with Cr, Mn, and Ti exhibiting remarkably small activation barriers (<0.1 eV; ~10 times lower than in the bulk). Calculations also show that the bulk diffusion mechanism and kinetics differ for oxygen and sulfur, with oxygen having a faster mobility and preferentially diffusing through the tetrahedral interstitial sites in Ni matrix, where it can be trapped in a local minimum.
Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99354, United States.
Vitaly
V
Alexandrov
Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99354, United States.
Maria L
ML
Sushko
Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99354, United States.
Daniel K
DK
Schreiber
Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99354, United States.
Stephen M
SM
Bruemmer
Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99354, United States.
Kevin M
KM
Rosso
corrosion; density functional theory; diffusion; grain boundaries; oxidation; stress corrosion cracking