| 摘要: | 研究期間：10108~10207;This proposal plans to tackle the multi-scale-collective mechanical behavior of the advanced metallic systems in two aspects: First, the theoretical description of the mechanical behavior of the metals on different lengths scales via in-situ neutron/synchrotron x-ray characterization and, Secondly, the implementation of the aforementioned theoretical description on molecular dynamics simulation to observe the microstructure evolution subjected to the simulated experimental environment. The selected advanced alloy systems are the bulk-metallic-glass-matrix composites (BMGMCs) and the nano-crystalline materials, which exhibit very unique mechanical properties. Both of the systems seem to be able to answer the long-waiting solution of the conflict between the strengths and the toughness. However, there are still drawbacks of each kind. The poor tensile ductility and chaotic-tension failure limit the practical applications of the typical BMGMCs. Meanwhile, the mechanical behaviors of the bulk nano-crystalline materials are not clear yet. The key issue is that the mechanical behavior of the advanced metallic systems is beyond the traditional understanding of the collective behavior of the coarse-grain alloys. Unknown multi-scale deformation mechanisms accompanying with the new-type local hierarchical structures evolve at different stages of the deformation levels. Hence, we need new characterization to observe the different behaviors, especially during the deformation. Moreover, the modeling is equally necessary to assist the understanding of the in-situ characterization. In this proposal, we assume that during the deformation, the evolution of the advanced-metal structure can be systematized in terms of homologous series of stacking variants of simple subunits or modules. In each of these groups, modules of structure are combined to form a number of closely related microstructure. Two questions must be resolved in order to explain the existence of these microstructure. First, why are specific modular observed? Modules must represent particularly stable topological arrangements of atoms, because they reappear in different systems. The reasons for the relative of these configurations, however, are not yet well understood. A second question is why are some specific arrangements of modules stable? The first-year objective of this proposal is to theoretically select some signature modules to define our newly-developed molecular dynamics system. Based on the above selection, we will refine neutron/synchrotron results accordingly. The goal of the second year of this proposal is to recursively find the self-consistent mechanisms combining both perspectives to create a new method to bridge the simulation and the characterization. The plan of the final year of this proposal is to design new alloy based on the accumulative understanding of the first-two-years results. Furthermore, the conduction of the granted NSC-supported Programs (99-2218-E-008-009 and 100-2221-E-008-041) has developed successful neutron and synchrotron x-ray characterization research team. We plan to continue applying the in-situ diffraction/scattering experiments to characterize both of the elastic and the plastic behavior of the advanced alloys. Combining with the molecular dynamics simulation, this is a new experimental-and-theoretical-modeling-joint approach. Overall, the proposed research will provide an excellent opportunity for the graduate and undergraduate students to participate in an experimental/computing synergistic research for both of the NSC Neutron and the future NSRRC Taiwan Light Source Projects. |
