X-ray Laue Microscopy to Understand Fatigue Damage (XMicroFatigue) – XMicroFatigue

The new X-ray microscope with depth resolution (3D-µLaue) allows the 3D mapping of microstructure and micro objects. 3D-µLaue is installed on the french beamline CRG-FI BM32 at the european synchrotron (ESRF) on the Laue micro-diffraction instrument. It complements the panel of characterization and metrological tools by X-ray scattering. The determination of the depth location of scattering signal relies on triangulation and differential computation from a series of scattering images recorded for several wire positions shadowing the scattered X-rays coming out sample. To accelerate the data acquisition, from 3 to 5 wires are used simultaneously and a new algorithm has been developed to reconstruct the scattering intensity as a function of depth with reduced noise. Measurements on controlled microstructures have validated the efficiency and the resolution. First scientific in situ studies were performed on single and bi-crystalline copper pillars by the german partner (MPIE-Düsseldorf). The interior location of stored defects and their density were evaluated in both cases.

The new X-Ray microscope with depth resolution (3D-µLaue) allows the 3D mapping of microstructure and micro objects. 3D-µLaue is installed on the french beamline CRG-FI BM32 at the european synchrotron (ESRF) on the Laue micro-diffraction instrument. It complements the panel of characterization and metrological tools by X-ray scattering. The determination of the depth location of scattering signal relies on triangulation and differential computation from a series of scattering images recorded for several wire positions shadowing the scattered X-rays coming out sample. To accelerate the data acquisition, from 3 to 5 wires are used simultaneously and a new algorithm has been developed to reconstruct the scattering intensity as a function of depth with reduced noise. Measurements on controlled microstructures have validated the efficiency and the resolution. First scientific in situ studies were performed on single and bi-crystal of copper pillars by german partner (MPIE-Düsseldorf). The interior location of stored defects and their density were evaluated in both cases.

Thanks to 3D X-ray Laue microscopy, Laue diffraction data can be fully exploited in difficult cases of real materials which are heterogeneous in depth (orientation and strain): e.g. in metallurgy, materials for energy or microelectronics. 3D-µLaue measurements can now be performed on demand to decompose the overall signal into depth contributions. The project funded a new X-ray detector with small readout time allowing higher recording rate (0.1 to 3 images/sec, volume 1To/day) and the design of a suited software automated analysis.

From first experimental measurements, 4 articles in prepared for publication about the microstructural evolution of single and bi-crystal pillars in situ deformed.
Preliminary results have already been presented in international conferences (EMMC 2017, ESMC 2018, ICSMA 2018, XTOP 2018) and french ones (Rayons X Matière 2017, 2019 et 2021 ; Colloque AFC 2017 et 2021; MATERIAUX 2018). The new X-ray detector is also mentioned in 4 published beamline users articles.

The objective of the XMicroFatigue project is to build a synchrotron based 3D x-ray microscope and combine it with a
state-of-the-art device for in situ deformation of objects at the micrometre length scale. This advanced characterisation tool
will provide unprecedented insights into the structural evolution of damage in materials under low cycle fatigue loading.
For this purpose, the Laue microdiffraction station at the French BM32 beamline at the ESRF will be upgraded to put the
performance at a higher level by achieving an additional sub-micrometre resolution along the sample depth. The so called
DAXM method will be accelerated enabling the investigation of a wide range of heterogeneous and complex materials
regarding their fundamental and industrial aspects, such as reliability and endurance. The fatigue damage accumulation
will be studied in the vicinity of well-selected grain-boundaries of micron-sized cantilevers in two distinct cases: close to a
free surface and in the material interior.
The x-ray microscope will measure 3D spatially-resolved microstructural quantities relevant to understand the underlying
interaction mechanisms between dislocation and grain-boundary, such as the deviatoric and hydrostatic strains, the
orientation and the density of the so-called geometrically-necessary-dislocations. Thereby, the project enables the
formulation of mechanism-based material laws, which brings us one step closer to the future of material science: grain-
boundary engineering. The two partners (INAC BM32 beamline and the nano- and micromechanics group of the MPIE)
have a recognised expertise in synchrotron based structural characterisation and in understanding the mechanical
behaviour of micron sized objects by in situ deformation.