Mesoscale Modeling of Grain Boundaries: From Segregation Phenomena to Faceting Instabilities

Owing to their nanometric feature size, the properties and stability of nanocrystalline (NC) materials are greatly influenced by interfaces, internal or free. In this presentation, we first begin with a brief introduction to mesoscopic treatments of materials microstructures, which serve as a building block for the quantitative modeling of a wide range of phenomena, such as grain growth, coarsening, sintering, segregation and phase transitions. The rest of the talk is then delivered in two parts; both of which cover the development of mesoscopic models aimed at unraveling the role of grain boundaries (GBs) on the stability of NC materials.   The first part is focused on GB solute segregation as a route to mitigate grain growth in NC metals and stabilize their grain structures. Regimes are identified, where the reduction in GB energy, and thus the driving force for grain growth, is significant. The discussion will then focus on immiscible alloys, where the enhanced stability is a manifestation of the competing effects of GB segregation and bulk phase separation.  

In the second part, we turn our attention to interface anisotropy, where cusps in the GB energy may exist as a function of GB inclination. Therefore, an initially flat GB may facet into hill-and-valley structures with well-defined planes and junctions connecting them. We investigate GB faceting and highlight the role of junctions on facet coarsening dynamics. Within the context of continuum plasticity frameworks, such GB re-construction processes can greatly influence dislocation-GB interactions and slip transmission behavior.