Grain boundary plane orientation is a profoundly important determinant of character in polycrystalline materials that is not well understood. This work demonstrates how boundary plane orientation fundamental zones, which capture the natural crystallographic symmetries of a grain boundary, can be used to establish structure-property relationships. Using the fundamental zone representation, trends in computed energy, excess volume at the grain boundary, and temperature-dependent mobility naturally emerge and show a strong dependence on the boundary plane orientation. Analysis of common misorientation axes even suggests broader trends of grain boundary energy as a function of misorientation angle and plane orientation. Due to the strong structure-property relationships that naturally emerge from this work, boundary plane fundamental zones are expected to simplify analysis of both computational and experimental data. This standardized representation has the potential to significantly accelerate research in the topologically complex and vast five-dimensional phase space of grain boundaries.

No abstract

With twin grain boundaries playing an important role in numerous materials, it is important to understand their behavior across the full range of possible boundary plane orientations. This work examines the migration of 41 computed ∑3 nickel grain boundaries over a range of temperatures. The boundary plane orientation appears to play the determining role in the nature of the migration observed, which is evident when the data are plotted in the fundamental zone of possible boundary plane orientations. GBs whose boundary plane lie between and exhibit thermally activated migration and the atoms do not move in a coordinated fashion. The remaining GBs, including the GB, exhibit some form of thermally damped migration. The thermally damped migration is characterized by inverse temperature dependence where the GBs migrate faster at lower temperatures and move in a coordinated fashion involving Shockley partial dislocations. The inverse temperature dependence, which is confirmed by random walk simulations, appears to be consistent with dislocation drag, which could be related to the Shockley partial dislocations. At least one GB exhibits mixed mobility trends due to the presence of both thermally activated and thermally damped migration characteristics.

This work details the additive friction stir-deposition (AFS-D) of copper and evaluation of its microstructure evolution and hardness. During deposition, a surface oxide is formed on the deposit exterior. A very fine porosity is formed at the substrate–deposit interface. The deposit (four layers of 1 mm nominal height) is otherwise fully dense. The grains appear to have recrystallized throughout the deposit with varying levels of refinement. The prevalence of twinning was found to be dependent upon the grain size, with larger local grain sizes having a higher number of twins. Vickers hardness measurements reveal that the deposit is softer than the starting feedstock. This result indicates that grain refinement and/or higher twin densities do not replace work hardening contributions to strengthen Cu processed by additive friction stir-deposition.

No abstract

No abstract

No abstract

No abstract