X-ray radiography is an absorption-based imaging technique. A series of radiographic images recorded in real time with an acceptable time resolution is known as radioscopy. It was successfully applied in recent years for investigations of diffusion and flow phenomena in liquid metals, solidification and metal foaming processes.
Figure 1: Principle of radiography
X-ray attenuation along path dx: dI = -µ·I·dx;
µ is X-ray attenuation coefficient / a function of X-ray energy and of the material (density, composition, phases…).
I = I0 exp(-µ·x) the Beer-Lambert law of attenuation or the Beer–Lambert–Bouguer law.
The X-ray radioscopy delivers a two-dimensional projection of the local density in the slit container corresponding to the distribution of the relative brightness P in the acquired images. For instance, this method provides a two-dimensional visualisation, revealing transient changes in the local composition of the solidifying In-Ga alloy. An estimate of the flow field ahead of the solidification front has been obtained by analyzing the motion of brightness contours corresponding to gradients in the solute distribution (Fig 2a). Other interesting application concerns the field of liquid metal two-phase flows focusing on bubble formation or bubble motion in a bulk liquid (Fig. 2b).
Figure 2: a) Snapshot of the dendritic structure with reconstructed melt flow using the Optical Flow approach; b) Bubbly flow – raw image and after data processing.
Shevchenko, N.; Roshchupkina, O.; Sokolova, O.; Eckert, S.
The effect of natural and forced melt convection on dendritic solidification in Ga-In alloys
Journal of Crystal Growth 417(2015), 1-8
Keplinger, O.; Shevchenko, N.; Eckert, S.
Validation of X-ray radiography for characterization of gas bubbles in liquid metals
IOP Conference Series: Materials Science and Engineering 228(2017), 012009
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
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
Met. Mater Trans A. 39A (2008) 613–623