X ray Tomoscopy Time resolved Microtomography for Materials Science

Time resolved in situ and operando microtomography is increasingly moving into the focus of materials research. Recent improvements in temporal and spatial resolution allow for detailed image analyses of fast phenomena and processes in 4D. The work was performed at our own facility at the EDDI beamline, Bessy II, Berlin, Germany as well as at the TOMCAT beamline, Swiss Light Source, Villigen, Switzerland. The setup and sample environment are composed of a fast and precise rotating stage and contactless IR heating of X ray transparent crucibles made, e.g., of boron nitride, into which samples are placed. We applied X ray tomoscopy with acquisition rates of up to 1000 tomograms per second and spatial resolutions in the micrometer range. We show how such approach can be combined with simultaneous energy dispersive diffraction, which is of special interest in cases where structural or morphological changes are correlated with chemical reactions or phase transformations. Some recent results and case studies include i Analyses of the evolution of the structure and density of liquid metal foams, where knowledge about the mechanisms of bubble formation, growth and ageing over a long period of time are gained and quantitative analyses of bubble parameters with millisecond temporal resolution can be derived. ii The immiscible hypermonotectic reaction of AlBi10 in wt alloy. iii Dendrite evolution in AlGe10 in wt casting alloy during fast solidification. iv The combustion process and the evolution of the constituents in a burning sparkler. v The evolution of metallic samples during laser processing in particular laser welding and additive manufacturing of metal

In situ observation with x ray for tentative exploration of laser beam welding processes for aluminum based alloys

In recent years, laser processes have taken an everincreasing market share in the manufacture of components. The development of new, improved beam sources with corresponding systems technology and the decreasing investment costs of the beam sources are important keys for this success. Especially high frequency beam oscillation has a great potential in laser beam welding and cutting. The main obstacle for the widespread breakthrough of high frequency beam oscillation is the still insufficient understanding of the underlying physical mechanisms. Gaining a deeper insight is essential for process optimization. The in situ observation with X ray enables the visualization and analysis of these highly dynamic processes inside the workpiece. The goal of the performed experiment described in this paper was to insitu analyze the structural evolution of and defect generation in laser welding beads of different aluminum alloys. A fiber laser max. 600 W, cw output power including a beam scanner control system for rapid beam guidance was used. Of general interest was the comparison between static and oscillated beam guidance and the effects on the joining procedure. The paper shows first results of the analysis of the melt pool behavior and seam formation as well as the formation of seam irregularities during the laser process. In the simplest case, radiographs were taken, i.e. 2D projections of the X ray absorption coefficient distribution within a material. Thereby recordings from 10000 up to 40000 fps could be generated. Furthermore, tomoscopies the continuous acquisition of tomographic 3D images up to 100 tomograms per second could be generated with proven equipment, whose main components are a high speed rotation stage and camera system. The findings will help to get a better understanding of keyhole phenomena as well as effects of turbulent melt flow such as pore formation and guide to solutions for preventing them. Hence first results for high frequency beam oscillation processes including melt pool degassing and porosity reduction will be shown and discussed. Introductio