Energetics and Deformation Response of Random Grain Boundaries in FCC Nickel

Molecular dynamics simulations are use to study the energetics and deformation response of random grain boundaries in polycrystalline Nickel. Computer generated samples of defect-free Ni were created, plastically deformed, and examined as a baseline understanding to the underlying mechanisms of deformation and intergranular fracture in FCC metals. Two types of samples were utilized: a sample with columnar grains consisting of pure <110> tilt boundaries and a thin-film sample with 3D grain orientations modeled after an experimental sample of austenitic steel. The structure and energies of these random boundaries under stress and temperature was analyzed. Heterogeneous displacement maps were made for a side-by-side comparison of the dislocation activity and interactions with the grain boundaries. The dislocation behavior was found to be consistent between the two digital sample types and further comparison with experimental samples was made. The intergranular cracking behavior was also studied and various factors were examined to generate general trends. Crack initiation was observed to typically occur in random high-angle boundaries close to a triple junction where the cracks have high angles with respect to the tensile loading direction. The cracking results from the simulations agree well with current preliminary results of experimentally deformed austenitic steel samples. Furthermore, the behavior and failure of the thin-film sample is compared with its corresponding experimental sample.