Large-scale Phase-field Studies of Three-dimensional Dendrite Competitive Growth at the Converging Grain Boundary during Directional Solidification of a Bicrystal Binary Alloy

Abstract

Large-scale phase-field studies of three-dimensional (3D) dendrite competitive growth at the converging grain boundary (GB) of a bicrystal binary alloy were carried out using the GPU-rich supercomputer TSUBAME 2.5 at Tokyo Institute of Technology. First, a series of thin-sample simulations were performed to investigate the effects of thin-sample thickness, unfavorably oriented (UO) grain inclination angle, and dendrite arrangement on an unusual overgrowth phenomenon whereby the favorably oriented (FO) grain is overgrown by the UO grain. It was concluded that the unusual overgrowth easily occurs as the thickness of the thin sample and the UO grain inclination angle decrease. It was also concluded that the interaction between FO and UO dendrites at the converging GB depends on the dendrite arrangement for relatively large dendrite spacing. Next, realistic large-scale simulations whereby multiple dendrites interact at the converging GB were performed. Unusual overgrowth was also observed in such large-scale simulations, and this phenomenon easily occurred at smaller UO dendrite inclination angles. Furthermore, it was also concluded that the FO and UO dendrites rearrange toward a space-to-face interaction. Because the interaction between FO and UO dendrites differs according to the location on the GB, a zigzag GB was formed, especially at small UO grain inclination angles.

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“…It was successfully applied to the very‐large‐scale phase‐field simulation with 4096 × 4104 × 4096 grid points and 4 × 10 6 time steps, which might be the largest phase‐field simulation even now. After that, we have developed a multi‐GPU code for the quantitative phase‐field model to simulate the directional solidification of a binary alloy, and the competitive growth among multiple dendrites were investigated in single‐crystal, bicrystal, and polycrystal …”

“…The FO grain is gradually selected by repeating this process . We have also performed the 3D phase‐field simulations for a bicrystal binary alloy . In the thin sample simulations, we changed sample thickness and FO dendrite arrangements as the FO and UO dendrite interaction at the converging grain boundary becomes face‐to‐face and space‐to‐face.…”

“…We have also performed the 3D phase‐field simulations for a bicrystal binary alloy . In the thin sample simulations, we changed sample thickness and FO dendrite arrangements as the FO and UO dendrite interaction at the converging grain boundary becomes face‐to‐face and space‐to‐face. In the case of the face‐to‐face interaction, the unusual overgrowth occurred independent of the sample thickness and easily occurred for thinner sample than the thick one.…”

“…However, the UO dendrites penetrated between the FO dendrites when the sample thickness became larger than a critical thickness. We also performed the bicrystal competitive growth simulations in a bulk sample with multiple dendrite interactions . The simulations were performed by parallel computation using 386 GPUs (K20X) for a domain with 768 Δx × 1536 Δx × 1536 Δx ( Δx = 0.75 μm).…”