Nanosegregation, Microtexture and the Control of Brittle Failure

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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.***