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- Radiography (2) (entfernen)
A x-ray radioscopy technique for measuring in situ chemical diffusion coefficients in metallic melts
is presented. The long-capillary diffusion measurement method is combined with imaging
techniques using microfocus tubes and flat panel detectors in order to visualize and quantitatively
analyze diffusive mixing of two melts of different chemical composition. The interdiffusion
coefficient as function of temperature and time is obtained by applying Ficks diffusion laws.
Tracking the time dependence of the mean square penetration depth of the mixing process allows to
detect changes in the mass transport caused by convective flow. The possibility to sort out
convective mass transport contributions from analysis enhances significantly the accuracy compared
to the conventional long-capillary diffusion measurement method with postmortem analysis. The
performance of this novel diffusion measurement method with x-ray radiography technique is
demonstrated by a diffusion experiment in an Al-Ni melt.
In situ crack detection in the mushy zone and the solid weld of a gas tungsten arc (GTA) weld using X-ray imaging during welding is a new research area for NDT inspection. Usually, NDT flaw detection is done after the complete solidification of the weld seam. In this paper, we present the use of real-time radiography with a minifocus X-ray source (YXLON X-ray tube Y.TU 225-D04) and a 75μm pixel size digital detector array (Dexela 1512) for the acquisition of 2D radiographic images by a sequence of exposures with time intervals of 80 ms for hot crack detection during single pass bead-on-plate GTA welding of 3 mm thick plates of aluminium alloy AlMgSi (6060). An analysis of the crack distribution in the weld sample is conducted from the acquired 2D radiographs and its corresponding 3D volumetric reconstruction achieved by linear coplanar digital laminography.
This in situ approach opens new possibilities in the field of hot crack research by having the direct information of both the crack initiation and growth and its correlation to the welding parameters.