Nanocrystalline (nc) materials, i.e. polycrystalline structures with grain sizes below 100 nm exhibit extraordinary properties strength. As a first assumption, such property derives from the short paradigm “smaller is stronger”. For grain sizes below 50 nm deformation mechanisms usually involve a quasi-stationary balance between dislocation slip and grain boundary mediated mechanisms. But there is still an ongoing debate, which one of these mechanisms governs the deformation behavior of nc metals [1,2].
Therefore determination of grain size, analysis of the local texture and characterization of grain boundaries in nanocrystalline materials are crucial. Different techniques have been tested, such as automated crystal orientation mapping in Transmission Electron Microscopes (TEM) . But they suffer a lack of accuracy due to the nanocrystalline nature of tested specimen. Grain overlapping, for instance, trends to observe smaller grains. By x-ray diffraction, it is also possible to determine grain size, but measurements provide size of coherent domains only that we consider equal to grains.
In this framework, a new technique based of Transmission Kikuchi Diffraction (TKD) has been been recently introduced as a Scanning Electron Microscope (SEM) based method capable of giving orientation maps as the EBSD method but with a spatial resolution improved by up to one order of magnitude . The technique requires a specimen thin enough to be transparent to the electron beam. In the current configuration, it uses hardware and software developed for the EBSD technique. We proposed a new configuration of the TKD where the detector is disposed horizontally on the axis of the microscope instead of being vertically positioned as in the conventional configuration (see Figure). This achieves better spatial resolution and angular resolution than the ones of the current TKD configuration . Moreover, acquisition times are shorter than in the conventional technique, because the intensity of the forward scattered electrons is much higher than that of the large angle scattered electrons.
Firstly, technological challenges such as technique design will be presented. Secondly first results on electrodeposited nanocrystalline nickel will be discussed and they clearly show the full potentialities of this original characterization set-up.
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To cite this abstract:Antoine Guitton, Julien Guyon, Yudong Zhang, Emmanuel Bouzy; Grain size determination in nanocrystalline materials using the TKD technique. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/grain-size-determination-in-nanocrystalline-materials-using-the-tkd-technique/. Accessed: December 6, 2022
EMC Abstracts - https://emc-proceedings.com/abstract/grain-size-determination-in-nanocrystalline-materials-using-the-tkd-technique/