Corrosion of metal surfaces and interfaces in molten salt systems stands as one of the largest remaining obstacles that must be overcome before a viable molten salt reactor can be realized. In Cr containing Ni-based superalloys, envisioned for use in the structural and piping components of these systems, the dominant form of corrosion is the depletion of Cr atoms near the surface and along grain boundaries. At this moment, the mechanisms underlying Cr depletion are not fully understood, and the challenges associated with studying molten salts make it unlikely an answer will be found experimentally without considerable time, effort, and cost. Carefully devised computational modelling may lessen this burden by providing acumen and insight that could help narrow the range of possible reaction pathways. In this work, density functional theory (DFT) is employed to model the effect adsorbed salts atoms have on the surface segregation of a Cr atom in an fcc Ni matrix. Surface segregation energies describe the energetics associated with the location of a solute atom near a surface (i.e. the relative energy of an atom when its located in the bulk versus at the surface). Calculations show that under a clean surface (i.e. no adsorbed salt atoms) it is energetically favorable for the Cr atom to inhabit the 3rd or 2nd surface layer, but largely unfavorable for it to sit in the outermost 1st layer. When a Cl or F atom is adsorbed to the surface the segregation energy to the 1st layer decreases considerably, suggesting the adsorption of salt atoms increases the likelihood of a Cr atom segregating to the surface. Comparison of these effects with other potential adsorbates, such as O or OH may help to unriddle the mystery underlying Cr depletion. This talk will report new insights into material-salt interfaces through atomistic modeling.

Surface segregation behavior in molten salt facing Ni-Cr alloys: First principles investigation

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.