Contact

Dr. Natalia Shevchenko
Magnetohydrodynamics
n.shevchenkoAthzdr.de
Phone: +49 351 260 - 3313

Dr. Sven Eckert
Head Magnetohydrodynamics
s.eckertAthzdr.de
Phone: +49 351 260 - 2132, 3563
Fax: 12132, 2007

X-ray radioscopic visualisation of solidifying metallic melts

S. Boden, B. Willers, S. Eckert, G. Gerbeth


Objectives

  • Experimental assessment of the solidification process in opaque metal alloys
  • Investigation of the fundamental mechanisms how melt convection affects the solidification
  • Providing qualified knowledge on how tailored melt flow control techniques can modify the properties of the solidified material

X-ray radioscopy

  • Non-invasive, contactless imaging method enabling real-time and in-situ observation of the solidification front and with a spatial resolution of a few microns
  • Two-dimensional X-ray shadow image provides information on the density and composition variations in the sample

Fig. 1: Radioscopic setup

Materials, methods and results

Solidification experiment

  • Ga-30wt%In, a binary metal alloy with low melting point, provides sufficient X-ray attenuation contrast between the separated phases
  • The alloy was contained in a flat solidification cell (150 µm gap width), which was aligned in parallel with gravitation
  • By means of a heating/cooling device the alloy was directionally solidified from below

Fig. 2: Schematic depiction of the solidification experiment

Image processing

  • Pre-processing involves noise-filtering and brightness-to-composition mapping
  • Optical flow (motion field of brightness patterns between consecutive image frames) computation delivers inform-ation on the flow velocities in the melt

Fig. 3: Growth of in-crystals accompanied by the rejection of solute in the formation of large plumes of Ga-enriched melt

Experimental results

  • Visualisation of
    - Dendritic growth of In-2wt%Ga crystals
    - Solute rejection and local accumulation
  • Formation of unstable density stratification
  • Strong correspondence between melt convection and crystal growth
  • Modification of the diffusion layer ahead of the solidification front
  • Transport of fresh melt towards the mushy zone accelerates growth
  • Accumulation of solute-rich melt decelerates crystal growth
  • Local temporal re-melting triggered by solutal undercooling
  • Convection affects the selection between primary and secondary arm growth

Fig. 4: Detailed view of the crystal formation during the directionaly solidification of the Ga-30wt%In alloy. Vector arrows represent the computed optical flow field

Perspectives

  • Validation of results from computational micro-structure simulations of the solidification process
  • Elucidation of the effects of electromagnetically forced melt-convection on the crystal growth
  • Clarification of the dendritic fragmentation process

Radioscopic visualisation of bubble motion in liquid metals

Objectives

  • Background from metallurgy and process engineering: Melt refining and melt stirring by gas bubbling
  • Radioscopy provides information on bubble formation, shape evolution and motion trajectories
  • Results will be useful for the evaluation of analytical and computational liquid metal two-phase flow models

Fig. 5: Bubble motion in liquid metal GaInSn, channel depth: 12 mm

References

Peer-reviewed journals

  • Boden, S.; Eckert, S.; Willers, B.; Gerbeth, G.: X-ray radioscopic visualization of the solutal convection during solidification of a Ga-30 wt pct In alloy, Metall. Mater. Trans. A 39 (2008) 613-623, doi:10.1007/s11661-007-9462-5
  • Boden, S.; Willers, B.; Eckert, S.; Gerbeth, G.: Observation of dendritic growth and fragmentation in Ga-In alloys by X-ray radioscopy, Int. J. Cast. Metal. Res. 22 (2009) 30-33, doi:10.1179/136404609X367263
  • Boden, S.; Eckert, S.; Gerbeth, G.: Visualization of freckle formation induced by forced melt convection in solidifying GaIn alloys, Mater. Lett. 64 (2010) 1340-1343, doi:10.1016/j.matlet.2010.03.044
  • Shevchenko, N.; Boden, S.; Eckert, S.; Gerbeth, G.: Observation of segregation freckle formation under the influence of melt convection, IOP Conf. Series: Mater. Sci. Eng. 27 (2011) 012085, doi:10.1088/1757-899X/27/1/012085
  • Shevchenko, N.; Eckert, S.; Boden, S.; Gerbeth, G.: In situ X-ray monitoring of convection effects on segregation freckle formation, IOP Conf. Series: Mater. Sci. Eng. 33 (2012) 012035, doi:10.1088/1757-899X/33/1/012035
  • Fröhlich, J.; Schwarz, S.; Heitkam, S.; Santarelli, C.; Zhang, C.; Vogt, T.; Boden, S.; Andruszkiewicz, A.; Eckert, K.; Odenbach, S.; Eckert, S.: Influence of magnetic fields on the behavior of bubbles in liquid metals, Eur. Phys. J. Special Topics 220 (2013) 167-183, doi:10.1140/epjst/e2013-01805-4
  • Shevchenko, N.; Boden, S.; Eckert, S.; Borin, D.; Heinze, M.; Odenbach, S.: Application of X-ray radioscopic methods for characterisation of two-phase phenomena and solidfication processes in metallic melts, Eur. Phys. J. Special Topics 220 (2013) 63-77, doi:10.1140/epjst/e2013-01797-y

Conference proceedings

  • Boden, S.; Willers, B.; Eckert, S.; Gerbeth, G.: Visualisation of the concentration distribution and the flow field in solidifying metallic melts by means of X-ray radioscopy, Proceedings of the 5th Decennial International Conference on Solidification Processing, Sheffield, UK, 2007, 311-315
  • Boden, S.; Willers, B.; Eckert, S.; Gerbeth, G.: X-ray visualisation of solidifying GaIn-alloys in the presence of melt convection, Proceedings on the 6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Germany, 261-264
  • Boden, S.; Eckert, S.; Gerbeth, G.; Simonnet, M.; Anderhuber, M.; Gardin, P.: X-ray visualisation of bubble formation and bubble motion in liquid metals, Proceedings on the 6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Germany, 387-390

Contact

Dr. Natalia Shevchenko
Magnetohydrodynamics
n.shevchenkoAthzdr.de
Phone: +49 351 260 - 3313

Dr. Sven Eckert
Head Magnetohydrodynamics
s.eckertAthzdr.de
Phone: +49 351 260 - 2132, 3563
Fax: 12132, 2007