Atomistic Theory and Computer Simulation of Grain Boundary Structure and Diffusion

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9753243 Farkas This project is aimed at theoretical investigations and computer simulations of point defects and grain boundaries, as well as diffusion in the lattice and along grain boundaries in ordered compounds. The focus of research will be the intermetallic compound NiAl. The project includes collaborations with groups working on ab initio calculations and on diffusion experiments. Atomic structure and diffusion along grain boundaries in intermetallic compounds are of great interest in connection with their limited ductility and high-temperature creep resistance. Grain boundary diffusion in NiAl has never been studied experimentally or theoretically. Moreover, correct atomistic calculations of grain boundary diffusion coefficients have only become possible recently due to work done by the proposers on the jump correlation theory and the development of the respective simulation methods. These theory and simulation techniques will be further improved and applied to grain boundaries in NiAl. Angular-dependent semi-empirical potentials of the embedded- atom type will be developed for NiAl by fitting to both experimental properties and to the results of ab initio calculations. The atomic structure for 001 and 011 symmetrical tilt grain boundaries will be calculated using molecular statics and dynamics. The formation energies and equilibrium concentrations of point defects in the lattice and in the grain boundaries will be calculated. The atomic migration energies by different mechanisms in the lattice and in the grain boundary cores will also be calculated. The point defect concentrations and migration energies obtained will be used for the calculation of lattice and grain boundary diffusion coefficients of Ni and Al using novel methods of jump correlation theory and the Monte Carlo method. The diffusion coefficients obtained will be compared with the experimental data obtained from experimental collaborators. NiAl will thus become the first ordered system, probably even the first binary system, where diffusion of both species in the lattice and along the grain boundaries will be studied by both experimental and theoretical methods. %%% This project is aimed at theoretical investigations and computer simulations of point defects and grain boundaries, as well as diffusion in the lattice and along grain boundaries in ordered compounds. The focus of research will be the intermetallic compound NiAl. The project includes collaborations with groups working on ab initio calculations and on diffusion experiments. NiAl will thus become the first ordered system, probably even the first binary system, where diffusion of both species in the lattice and along the grain boundaries will be studied by both experimental and theoretical methods. ***