Abstract
Time-resolved in situ tomography of dendritic growth in Fe–0.45 mass% C carbon steel was performed using synchrotron radiation X-rays at SPring-8 synchrotron radiation facility (Japan) with improvement of the image quality using a physics-based filter. The voxel size of the reconstructed image was approximately 6.5 μm × 6.5 μm × 6.5 μm, and the time resolution (duration of 360° rotation) was 4 s (0.25 rps). Three-dimensional images of the dendrites were reconstructed even without image processing; however, the low contrast resolution in Fe–C alloys led to poor image quality. Consequently, it was impossible to precisely track the solid/liquid interface or evaluate the average curvature. To improve the image quality, a physics-based filter (a PF filter) was developed using a phase-field model. In the PF filter, images were retrieved in terms of interface curvature. The PF filter significantly improved the computed tomography image quality. As a result, dendritic growth was clearly observed even in Fe–C alloys. Moreover, the average curvature of the solid/liquid interface was evaluated as a function of solidification time (solid fraction). The ability to systematically characterize growing dendrites will be beneficial for modeling and simulation of solidification phenomena.
Highlights
Time-resolved in situ observations using synchrotron radiation X-rays with high brilliance and high coherency have allowed us to observe solidification and related phenomena such as the solidification of low-melting-temperature alloys (Sn, Zn, and Al alloys) [1,2,3,4,5] and high-melting-temperature alloys [6,7,8,9,10,11]. These direct observations are beneficial for understanding microstructural evolution and casting defect formation as well as for constructing physical models, enabling, for example, the direct observation of the massive transformation in Fe–C alloys [9]
Dendrite arms were visible in the reconstructed images, as shown in Fig. 2(b), it was impossible to smoothly track the solid/liquid interface
The specimen was rotated at 0.25 rps, and 200 projections over 180° rotation were used for the reconstruction
Summary
Time-resolved in situ observations using synchrotron radiation X-rays with high brilliance and high coherency have allowed us to observe solidification and related phenomena such as the solidification of low-melting-temperature alloys (Sn, Zn, and Al alloys) [1,2,3,4,5] and high-melting-temperature alloys (cast iron, carbon steel, and stainless steel) [6,7,8,9,10,11] These direct observations are beneficial for understanding microstructural evolution and casting defect formation as well as for constructing physical models, enabling, for example, the direct observation of the massive transformation in Fe–C alloys [9]. This massive transformation was observed in Fe–Cr–Ni alloys [14]
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