Nanosegregation, Microtexture and the Control of Brittle Failure

这项资助使用了一种新的实验技术组合来确定局部微结构和纳米级杂质到晶界的分离之间的相互作用，这可能会导致脆性破坏。到目前为止，还没有研究过这种相互关系，但分析电子显微镜中的X射线图谱提供了对同一标本中多个未受干扰的边界(即在研究之前未破裂)进行定量分析所需的高空间分辨率和原子水平检测。透射式电子显微镜的自动结晶学可以确定跨越相同边界的取向错误。假设局部织构可以控制偏析的数量和程度，反之，偏析可以控制局部微观织构。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剂的有害影响，这是研究的主要目的。偏析成分分布的变化将通过在定制的衬底上形成薄膜或通过晶界工程产生的特定织构进行测量，晶界工程将产生高比例的低能晶界，使偏析最小化。将研究铜和铁的理想分离系统。%这项研究的一个更广泛的影响是，如果研究成功，它可能会提供一种替代目前(和昂贵的)做法的方法，将不需要的微量元素减少到不会导致脆化的水平。如果晶界工程可以最大限度地减少偏析，那么用来开发所需性能的热机械处理可以被修改以同时抑制偏析，从而使脆性边界的连通性降低到足以防止导致脆性破坏的裂纹扩展的水平。开发的技术将被纳入课堂教材、一本主要教科书的第二版以及利哈伊为工业和政府研究人员开设的年度显微镜课程。

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.***