Computer Simulation of Asymmetric Grain Boundaries and their Interaction with Vacancies and Carbon Impurity Atoms

Computer simulation has proven to be a powerful tool for determination of atomistic structure in complex zones in metals. This method has been applied to study asymmetric tilt boundaries in γ-iron and their interaction with vacancies and carbon atoms. A program, “GRAINS”, which employs classical equations of motion was used for these experiments. A first neighbor function described the interaction between atom pairs. Volume forces were imposed by the computational cell boundaries. Observations and conclusions of particular interest were: The determination of values for migration and formation energies of vacancies in the vicinity of a grain boundary so vacancy transport and diffusion mechanisms in the boundaries can be estimated more accurately. These values were found to differ appreciably from those in ordered regions. The zone of interaction extends into the grains along close-packed lines from misfit regions much farther than would be anticipated from measurements of grain boundary width. Local ordering in the misfit region of a grain boundary caused by a very few impurity atoms which demonstrated how trace concentrations of impurities could significantly affect the strength of a metal.