| Popis: |
In this reporting period, processing of nanostructured powders, consolidation of nanostructured powders, computer simulation, micro structural characterization, and mechanical deformation tests were carried out. The nanostructured powders and bulk nanostructured materials were produced successfully via optimization of processing parameters. The observed highly grain stability can be explained by a grain boundary pinning mechanism arising from the dispersoid particles as well as impurity segregation. The microstructures of the as- extruded and the deformed bulk nanocrystalline aluminum alloys were investigated using transmission electron microscopy. A nanoindentation technique and traditional mechanical tests as well as computer simulation were also used to evaluate the mechanical performance. A discrete dislocation dynamics model has been developed to bridge the gap between atomic simulations and continuum approaches. It has the potential to provide a rigorous description of the complex relationships between the macroscopic mechanical behavior of materials and the underlying fundamental physical mechanisms. The tensile test results showed that grain size effects, solid solution strengthening, Orowan strengthening and dislocation strengthening contribute significantly to the properties of the cryomilled Al alloys. The future work for the next period is also discussed in the report. |
