| 摘要: | 金屬材料是最重要的結構材料，但在交通等須考量載具重量與能源效率的應用時，金屬材料的strength/weight ratio 不如陶瓷、碳纖維以及高強度的高分子材料。相對於上述取代金屬於結構應用的材料，金屬的韌性(fracture toughness)，異向性控制，導電/熱以及高溫時的機械性能，卻又是其他材料所無法取代的。因此，如何藉由微結構的設計，以推進金屬材料的strength/weight ratio 成為重要的課題。為了更深入的研究微結構在破壞時的形變機制，使用臨場即時量測可直接提供同一時刻/同一樣品與環境參數間的關係。本計劃預計應用臨場即時中子/同步輻射繞射實驗，觀測在改變巨觀的機械應力/應變下，材料微結構的反應。透過繞射的實驗推算出晶格的應變。同時，透過對繞射峰形的分析推估塑變所造成的微結構變化。由這兩個微觀尺度的資訊，再進一步和巨觀機械性能與隨之而來的吸(放)熱量測做計算，進而了解形變過程中，以塑變形式儲存的形變量，為將來研發新材料建立基礎。本計畫將執行一年，將把參與本計畫之一位博士研究生、兩位碩二研究生與三名新進碩一學生分成兩個小組，分別探討不同金屬系統的拉伸與疲勞形變機制。本計劃建立的量化資訊將有利於未來先進結構材料之設計。本計劃將訓練學生貢獻於台灣光源與國科會之中子研究計畫。 Modern technologies strongly rely on the unique properties of metals, such as the best mechanical properties at temperatures up to a few hundred degrees, much higher fracture toughness, and isotropy. Increasing the strength of metals without sacrificing other properties is the urgent call for the advanced metals. Multi-scale hierarchical structures might be a possible optimization to improve the strength/weight ratios of the metals. The structures of complex metals 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 many different compounds. The reasons for the relative of these configurations, however, are not yet well understood. A second question is why are particular arrangements of modules stable? The objective of this proposal is to experimentally measure and to theoretically calculate the thermomechanical behavior of the selected metallic systems to address these questions. A key to understand the stability limits of various modular stacking arrangements may lie in structural variation of individual modules with temperature, pressure, and composition. In the NSC-supported Program (NSC99-2218-E-008-009), neutron and synchrotron x-ray structure determination have led to empirical relationships for the variation of atomic-bond distance and microstructure with the deformation levels. The diffraction results yielded both the elastic interactions from the diffraction-peak-position evolution and the plastic information from the evolution of the peak profile, respectively. The methodology to apply the neutron and synchrotron x-ray experiments has been developed. In the current proposal, the microscopic variables will be compared with the bulk mechanical measurements. The heat evolution subjected to deformation will be described based on the microscopic damage accumulation. A joint experimental and theoretical modeling effort is proposed here to study the plasticity and interplay between the mechanical and thermal responses. First, by experimentally examining the behavior of the tensile deformation coupling the in-situ neutron diffraction, macrostructually-based thermal mechanical responses on crystal plasticity will be developed. Second, the validity of mechanical-deformation-induced thermal fluctuation for the metallic system will be examined, and a parametric map will be built to outline the dependence of the environmental temperature and deformation modes on the plasticity. Moreover, through the comparisons of the above two types of the deformation mechanisms, we can investigate the plasticity in terms of the microstructure mechanisms for the design of the future structural metallic materials. The ability to quantitatively describe the plasticity is a critical step towards a mechanistic understanding of deformation properties, as well as ductility and toughness enhancement methods of the advanced structural materials. 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 NSRRC Taiwan Light Source Projects. 研究期間：10008 ~ 10107 |
