Liquid metal penetration at grain boundaries: Characterization by synchrotron radiation micro-radiography and micro-fluorescence

The penetration of liquid metals into the grain boundaries (GB) of solid metals in the absence of external stress is a process which, in the case of some specific couples, can lead to severe embrittlement of the solid. We present in this paper two synchrotron radiation (SR) X-ray imaging techniques, which are well adapted for the non-destructive bulk characterization of this type of phenomena. Synchrotron radiation X-ray micro-radiography was used to characterize the liquid metal penetration kinetics in the Al/Ga system. It was shown that this modern variant of absorption radiogaphy provides sufficient spatial and temporal resolution to observe the penetration of sub-micrometric liquid Ga films into the grain boundaries of Al bicrystals. Synchrotron radiation X-ray micro fluorescence on the other hand is well suited for the element specific characterization of extremely dilute systems. At the expense of temporal and spatial resolution, this technique allows one to detect minute quantities of atoms, diffusing along the GB of solid metals.