Theoretical design of SCC resistant Ni-base alloy by a computational chemistry approach

Since plausible stress corrosion cracking (SCC) models have, to date, been considering mass transports and oxidation phenomena occurring at the interface of an alloy surface to the exposed environment, it is hypothesized that the addition of minor elements to lower the transport kinetics and form a stable oxide film would be beneficial in preventing SCC. In this current investigation, density functional theory, applied to a generalized gradient approximation calculation, has been used to study a small N1SMJ cluster and a 16 atom bulk model. Cluster model results indicated that Ti, Sc and Y have high oxidation and activation energy in comparison to a pure Ni cluster These elements were very effective in achieving stable passive film formation which could resist SCC. Substitutions of these elements revealed that the interatomic bond distance exhibits a very small elongation in the presence of interstitial oxygen atoms. The cluster model calculation primarily recommended three elements for Ni-base alloys. Ni and bimetallic bulks were then simulated. Bulk model oxidation energies have a tendency similar to cluster models. Mulliken population has shown the substituted atom increased the charge transfer forming a strong chemical bond. The DFT calculation suggested that Ti, Sc, and Y are susceptible to SCC for Ni-base alloy.