Title

3D-Laue micro diffraction to characterize fatigue damage in bi-crystalline micro cantilevers

Conference Dates

September 29-October 4, 2019

Abstract

Laue microdiffraction (µLaue) – a synchrotron based technique applying sub-micron sized (0.5x0.5µm²), polychromatic x-ray beams – has proven to shed unprecedented light onto the deformation behaviour of small volumes. So far, µLaue was used in situ as well as for 2D mapping to understand the tensile, compression and fatigue behaviour of metals. 3D-µLaue – also called “Differential Aperture X-ray microscopy” [1] – extend the capabilities of µLaue to achieve submicron 3D spatial characterization. An absorbing wire is moved between the sample surface and the detector. It is used to partially shadow the Laue pattern in order to reconstruct depth-resolved Laue patterns (see Fig.1). The achieved depth-resolution is in the order of 0.5µm³. In recent years we have adopted the 3D approach and coupled it with an in situ deformation rig.

In this work we present the in situ characterization of low cycle fatigue damage in focussed ion beam (FIB) milled, micron sized copper single and bi-crystalline cantilevers (5x5x25µm³). Each bi-crystalline sample contains one single grain boundary located at the neutral plane. The experiments were performed at BM32 of the European Synchrotron (ESRF), using a combination of a micro straining rig and 3D-µLaue. From the measurements the lattice orientation, deviatoric strain tensor and the density of unpaired dislocations are extracted with sub-micron resolution. This is done at several different deformation stages, i.e. after ¼, ½, ¾ and full cycle.

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