The Effect of Light-Element Impurity Atoms on Grain Boundary Diffusion in FCC Metals: A Molecular Dynamics Simulation

Abstract: The effect of carbon and oxygen impurity atoms on diffusion along the tilt grain boundaries with 〈100〉 and 〈111〉 misorientation axis in metals with FCC lattice was studied by the molecular dynamics method. Ni, Ag, and Al were considered as metals. Metal atom interaction was described by many particle Clery-Rosato potentials constructed within the framework of tight binding model. To describe interactions of light-element impurity atoms with metal atoms and impurity atoms, Morse pair potentials were used. According to obtained results, impurities in most cases lead to an increase in self-diffusion coefficient along the grain boundaries, which is caused by crystal lattice deformation near the impurity atoms. Therefore, additional distortions and free volume are formed along the boundaries, which is more expressed for carbon impurities. Moreover, with an increase in carbon concentration in the metal, an increase in coefficient of grain-boundary self-diffusion was observed first, and then followed by a decrease. This behavior is explained by aggregate formation of carbon atoms at grain boundary, which leads to partial blocking of the boundary. Oxygen atoms had smaller effect on diffusion along the grain boundaries, which is apparently explained by the absence of aggregates and lesser deformation of crystal lattice forming around impurity. The greatest impurity effect on self-diffusion along the grain boundaries among the examined metals was observed for nickel. Nickel has the smallest lattice parameter, and impurity atoms deform its lattice around itself more than aluminum and silver. Therefore, they create relatively more lattice distortions in it and additional free volume along the grain boundaries, which lead to an increase in diffusion permeability. Diffusion coefficients along the high-angle boundaries with misorientation angle of 30° turned out to be approximately two times higher than along low-angle boundaries with a misorientation angle of 7°. Diffusion along the 〈100〉 grain boundaries flowed more intensively than along the 〈111〉 boundaries. © 2019, Allerton Press, Inc.