Inter- and Intragranular Stress Determination with Kossel Microdiffraction in a Scanning Electron Microscope [chapter]

Raphaël Pesci, Karim Inal, Sophie Berveiller, Etienne Patoor, Jean Sébastien Lecomte, André Eberhardt
2006 Materials Science Forum  
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more » ... /hdl.handle.net/null Abstract. A Kossel microdiffraction experimental set up is under development inside a Scanning Electron Microscope (SEM) in order to determine the crystallographic orientation as well as the inter-and intragranular strains and stresses on the micron scale, using a one cubic micrometer spot. The experimental Kossel line patterns are obtained by way of a CCD camera and are then fully indexed using a home-made simulation program. The so-determined orientation is compared with Electron Back-Scattered Diffraction (EBSD) results, and in-situ tests are performed inside the SEM using a tensile/compressive machine. The aim is to verify a 50MPa stress sensitivity for this technique and to take advantage from this microscope environment to associate microstructure observations (slip lines, particle decohesion, crack initiation) with determined stress analyses. Introduction X-Ray Diffraction (XRD) is a non-destructive technique very efficient for stress determination of different orders corresponding to different scales (with various methods and instruments). The first order represents the macroscopic or the pseudo-macroscopic stress, where said stress is determined in the whole material or in different phases. The second order defines the average stress of the grain and the third one is devoted to the stress on the crystalline pattern scale (considering for example precipitates or dislocations). However, between these last two orders, given the growing complexity of materials and their applications, it is often necessary to determine stress on an intermediary scale: hence the development of Kossel microdiffraction on the micronic scale [1]. This is a local analysis tool similar to that used first by [2] , an X-ray imaging inside a SEM using a 2D detector, which enables to determine not only the crystallographic orientation, but more importantly the stress and strain states (and this for different crystalline materials). It is very promising because it offers technological progresses when compared to conventional methods such as "classical" XRD or EBSD. Indeed, this diffraction technique inside the SEM enables to determine the crystallographic orientation with a greater precision (higher wavelengths emitted), as well as inter-and intragranular stresses since the spot used is only about one cubic micrometer. It also allows to observe simultaneously the microstructure of the material and its evolution, in particular during in-situ tensile tests, and the analysis can be considered as quasi-instantaneous, since it only takes a few minutes. This means that it becomes possible to realize a stress mapping very quickly (for example along grain boundaries or inside one grain,
doi:10.4028/0-87849-414-6.109 fatcat:leomspljgrbjtov3tkoct4skyq