Computer modeling of interfaces in crystalline materials: Application to nickel-aluminum, gold and copper

Solid interfaces such as surfaces and grain boundaries (GBs) play a very important role in the structural, mechanical, and electronic properties of materials. Using a variety of advanced computing and simulation techniques coupled with robust embedded-atom method potentials, a range of solid interfaces are explored using the intermetallic compound nickel-aluminum as a model structural material and copper and gold as model electronic materials. Low-index surfaces in NiAl for the stoichiometric and Ni-enriched cases are investigated by grand canonical Monte Carlo (MC) simulations. Surface re-ordering and segregation is observed. Surface stresses and surface segregation in (110) NiAl free-standing thin films have been studied using MC simulations. The size effect of segregation at the surface is explained by the elastic deformation of the film in response to the surface stress. Grain boundary structure and segregation at Sigma3 GBs in NiAl using stoichiometric and Ni-rich compositions are studied by molecular statics and MC simulations. Ni-segregation is observed, resulting in transformation of the GBs to structures capable of accommodating higher Ni concentrations. The full range of possible inclinations in the family of Sigma11 [110] asymmetric tilt grain boundaries in copper is investigated and structural trends are established. Development of a non-Sigma11, low-index boundary is observed, giving rise to local rotation of the GB tilt angle accommodated by development of intrinsic stacking faults. A more general case of the 9R structure in low stacking fault energy materials is postulated. MD simulation of the family of ⟨110⟩ 90° asymmetrical tilt GBs in gold are presented and compared with high-resolution transmission electron microscopy observations of the same boundaries. The faceting behavior for this family of GBs is explored and it is shown that varying the inclination angle produces a variety of faceting behaviors.