Mesoscale modeling of vacancy-mediated Si segregation near an edge dislocation in Ni under irradiation

Abstract

We use a continuum method informed by transport coefficients computed using self-consistent mean field theory to model vacancy-mediated diffusion of substitutional Si solutes in FCC Ni near an $\frac{a}{2}[1\overline{1}0](111)$ edge dislocation. We perform two sequential simulations: first under equilibrium boundary conditions and then under irradiation. The strain field around the dislocation induces heterogeneity and anisotropy in the defect transport properties and determines the steady-state vacancy and Si distributions. At equilibrium both vacancies and Si solutes diffuse to form Cottrell atmospheres with vacancies accumulating in the compressive region above the dislocation core while Si segregates to the tensile region below the core. Irradiation raises the bulk vacancy concentration, driving vacancies to flow into the dislocation core. The out-of-equilibrium vacancy fluxes drag Si atoms towards the core, causing segregation to the compressive region, despite Si being an oversized solute in Ni.