Nanometric intergranular liquid layer penetration in the Al/Ga system: An X-ray projection microscopy investigation

The penetration of liquid Ga along the grain boundaries of Al bicrystals is analysed by synchrotron X-ray projection microscopy. Using Kirkpatrick–Baez focussing optics, a secondary X-ray source is produced of about 90 × 90 nm2 spot size and typical divergences of a few milliradians. By positioning the sample downstream this source, the spatial resolution detector limitation is overcome and the ultimate resolution is rather given by the secondary source size. The present investigation deals with one of the very first applications of such a microscope, currently under commissioning at the ID19 beamline of the European Synchrotron Radiation Facility (ESRF, Grenoble, France).In situ observations of the Ga penetration process reveal linear propagation of the penetration front accompanied by a continuous thickening of the Ga intergranular wetting layer. By combining sub-micron spatial resolution and in situ imaging capabilities it has been possible to characterize simultaneously the presence of nanometric penetration layers and, for the first time, associated continuous relative movement of the grains of final amplitude in agreement with the value of the saturated Ga layer thickness. The measured deformation of the bicrystal is compared to the predictions of elasto-plastic crack propagation under mode I loading conditions.