Nanosegregation, Microtexture and the Control of Brittle Failure

这项资助使用了一种新颖的实验技术组合来确定局部微观结构和纳米级杂质在晶界上的偏析之间的相互作用，这可能导致脆性破坏。到目前为止，这种相互关系还没有被研究过，但是在分析电子显微镜下的x射线成像提供了高空间分辨率和原子水平的检测，这对于定量分析同一标本中多个未受干扰的边界（即在研究之前未断裂）是必要的。透射电子显微镜的自动晶体学可以确定跨越相同边界的取向偏差。假设是局部织构可以控制偏析的数量和程度，或者相反，偏析可以控制局部微织构。通过这些新技术获得的理解将允许开发新的热机械处理，以减轻分离的有害影响，这是研究的主要目的。偏析分布的变化将在特定的织构中测量，这些织构要么是通过在定制的衬底上形成薄膜，要么是通过晶界工程产生高比例的低能边界，从而使偏析最小化。研究理想的Cu和Fe分离体系。该研究的一个更广泛的影响是，如果成功，它可能提供一种替代方法，以减少不需要的微量元素到分离不会导致脆化的水平，目前（和昂贵）的做法。如果晶界工程可以使偏析最小化，那么用于开发理想性能的热机械处理可以同时进行修改以抑制偏析，从而使脆性边界的连通性降低到足以防止裂纹扩展导致脆性破坏的水平。开发的技术将被纳入课堂教材，主要教科书的第二版和利哈伊的年度显微镜课程，为工业和政府研究人员

This grant uses a novel combination of experimental techniques to determine the interplay between local microtexture and nanometer-scale segregation of impurities to grain boundaries, which may cause brittle failure. This inter-relationship has not been examined to date, but X-ray mapping in the analytical electron microscope offers both the high spatial resolution and atomic-level detection necessary for quantitative analysis of multiple, undisturbed boundaries (i.e. not fractured prior to study) in the same specimen. Automated crystallography for the transmission electron microscope can determine the misorientation across the same boundaries. The hypothesis is that local texture can control the amount and degree of segregation or, conversely, that segregation can control the local microtexture. The understanding obtained via these new techniques would permit development of new thermo mechanical treatments to mitigate the deleterious effects of segregants and this is a primary aim of the research. The change in segregant distribution will be measured in specific textures produced either via thin film formation on tailored substrates or via grain boundary engineering which creates a high fraction of low energy boundaries to which segregation is minimized. Ideal segregating systems in Cu and Fe will be studied.%%%A broader impact of the research is that, if successful, it may offer an alternative method of the current (and expensive) practice of reducing undesirable trace elements to levels where segregation does not cause embrittlement. If segregation can be minimized by grain boundary engineering, then the very thermo-mechanical treatments used to develop desirable properties may be modified to suppress segregation simultaneously, to levels where the connectivity of brittle boundaries is lowered sufficiently to prevent crack propagation leading to brittle failure. The techniques developed will be incorporated into classroom teaching material, a 2nd edition of a major textbook and Lehigh's annual microscopy courses for industrial and government researchers.***