Shinji Sakane

Kyoto Institute of Technology · Faculty of Mechanical Engineering

The dendrite solidification process has been observed and simulated using state-of-the-art techniques, such as time-resolved X-ray tomography (4D-CT) and high-performance phase-field (PF) simulations. 4D-CT has enabled the direct observation of the 3D dendrite growth in opaque alloys. However, the spatiotemporal resolution is not sufficient for inv...

The effect of natural convection on dendrite morphology is investigated through three-dimensional large-scale phase-field lattice Boltzmann simulations using a block-structured adaptive mesh refinement scheme with the mother-leaf method in a parallel-GPU environment. The simulations confirmed that downward buoyancy enhances the growth of the primar...

Understanding the motion and growth behaviors of equiaxed dendrites during solidification is important for predicting macrosegregation. In this study, we develop a phase-field lattice Boltzmann (PF-LB) simulation method for the settling and growth of an equiaxed dendrite during the nonisothermal solidification of a binary alloy. The PF-LB computati...

In this study, a multi-phase-field (MPF) framework for predicting epitaxial grain growth in selective laser melting (SLM) additive manufacturing (AM) with multi-track and multi-layer scanning was developed. The spatiotemporal change in temperature was approximated using the Rosenthal equation, which provides a theoretical solution for the temperatu...

Numerical study on the effect of liquid flow on three-dimensional dendrite growth is still a challenging topic. Herein, high-performance phase–field lattice Boltzmann (PF-LB) simulations were performed to investigate the effect of natural convection on dendrite morphology and the possibility for causing fragmentation. Parallel computing in multiple...

The integration of phase-field (PF) simulations and in situ observations is a promising approach for understanding dendrite growth. In this study, a preliminary data assimilation system is developed to integrate PF simulations and in situ real-time X-ray radiography during the directional solidification of a binary alloy. In this system, only the r...

Time-resolved in-situ X-ray tomography and high-performance phase-field simulations are state-of-the-art approaches to clarifying dendrite solidification. However, major issues persist, such as the insufficiency of spatiotemporal resolution in experiments and lack of material properties in simulations. To overcome these issues, in this study, we de...

An effective permeability prediction method was developed by applying an adaptive mesh refinement (AMR) scheme to the lattice Boltzmann (LB) simulations to compute interdendritic liquid flow. The developed method can automatically create adaptive meshes for LB simulations based on dendrite morphologies obtained by phase-field (PF) simulations. The...

The deformation of solid–liquid coexistence regions strongly affects the formation of solidification defects in casting applications. Thus, understanding the mechanism of semi-solid deformation is crucial. This study used the multi-phase-field lattice Boltzmann model (MPF-LBM), which can simulate polycrystalline solidification with solid motion and...

Integrating phase-field simulations and in situ observation experiments is a promising approach to better understand dendrite growth during alloy solidification. To integrate simulations and experiments, we developed a data assimilation system using an ensemble Kalman filter for dendrite growth with liquid flow and solid motion. In this system, we...

Simulations of dendritic solidification involving melt convection and solid motion usually require a considerably higher computational domain than the dendrite size, whose computational efficiency with a uniform mesh is extremely low. In this study, to accelerate those two-dimensional simulations using the phase-field and lattice Boltzmann (PF-LB)...

The motion of the equiaxed grains plays an important role in macrosegregation. To simulate the motion of three-dimensional (3D) equiaxed dendrites growing in an undercooled melt, a large computational domain with small grids is required. In this study, we investigated the morphology and velocity of the settling dendrite and the growth velocity of i...

An array of columnar dendrites is important to the microsegregation and permeability of interdendritic liquid flow. In this study, an array of tilted columnar dendrites growing during the directional solidification of a binary alloy was investigated via large-scale phase-field simulation. The main conclusion is that the hexagonal array is the domin...

In the phase-field simulation of dendrite growth during the solidification of an alloy, the computational cost becomes extremely high when the diffusion length is significantly larger than the curvature radius of a dendrite tip. In such cases, the adaptive mesh refinement (AMR) method is effective for improving the computational performance. In thi...

In casting processes, semi-solid deformation induces serious solidification defects, such as segregations. In this study, semi-solid deformation is investigated in detail using the multi-phase-field lattice Boltzmann model developed in a previous study. Specifically, we evaluate the changes of local solid fraction caused by the Reynolds’ dilatancy,...

Accurate prediction of the material microstructure formed by additive manufacturing (AM) is key to improving the properties of metal AM products. In this study, a model to simulate the material microstructure formed during the powder bed fusion AM is investigated. In the model, melting and solidification due to laser scanning, liquid flow in melt p...

Dendrite morphology formed during solidification of alloys is largely affected by thermosolutal convection. Although the phase-field lattice Boltzmann (PF-LB) model has made it possible to reproduce dendrite growth with themosolutal convection, the large computational cost is a major problem. In this study, to accelerate the PF-LB simulation with t...

Accurate evaluation of dendrite growth is essential to improve the quality of cast products. The objective of this study is to develop a data assimilation system to integrate X-ray imaging observations and phase-field simulations of three-dimensional columnar dendrite growth in a thin film. Here, solid fraction in the thickness direction of the thi...

The formation process of equiaxed structures during alloy solidification is a complicated multiphysics problem as it includes solid–liquid phase transformations, transport of solute and heat, liquid flow, solid motion, solid–solid interactions, and grain growth after solidification completion. In this study, a multi-phase-field (MPF) model with the...

Three-dimensional grain growth behaviors under anisotropic (misorientation-dependent) grain boundary energy and mobility are investigated via phase-field simulations. Based on a multi-phase-field model and parallel graphics-processing unit computing on a supercomputer, very large-scale simulations with more than three million grains are achieved, e...

To perform accurate, stable, and efficient phase-field lattice Boltzmann (PF-LB) simulations of the solidification of alloys with melt convection, a two-relaxation-time (TRT) model for calculating the collision term in the LB equation and an interpolated bounce-back (IBB) model for imposing a non-slip condition at a solid-liquid interface—(TRT-IBB...

Prediction and control of dendrite growth is crucial for material properties. Phase-field method is widely used for the prediction of dendrite growth. Although the phase-field simulation of dendrite growth needs interfacial properties such as solid-liquid interfacial energy, mobility and these anisotropies, there are no those values for almost all...

In the casting process of alloys, semi-solid region is deformed due to the solidification shrinkage and/or external force, which causes serious solidification defects such as porosity, cracking, and macrosegregation. Better understanding of semi-solid deformation is crucial for reducing solidification defects. In this study, the multi-phase-field l...

Phase-field (PF) method is a powerful numerical model for predicting dendrite growth during solidification. Although some material properties are required to perform PF simulations, the lack of those properties, especially the interfacial properties such as interfacial energy and mobility, is a major issue in phase-field simulations. The ultimate g...

Permeability is a very essential parameter in simulations for predicting macrosegregation. In our previous study, we have developed the permeability prediction method using phase-field and lattice Boltzmann methods [Acta Mater. 164 (2019) 237-249, Acta Mater. 188 (2020) 282-287]. In this study, we evaluate the permeability for columnar dendrites wi...

Herein, three types of converging grain growth were investigated during directional solidification, through two-dimensional phase-field simulations. The three types were distinguished by the orientation of the favorably oriented (FO) dendrites. The growth orientation of the FO dendrites was parallel to the thermal gradient direction in type I, wher...

Permeability is a very important parameter determining fluid dynamics in macroscale casting simulations. For a columnar solidification structure, the permeability has anisotropy and becomes a tensor quantity. In our previous study, we proposed a permeability tensor and confirmed its validity. In this study, the applicability of the permeability ten...

Mechanisms of semi-solid deformation are crucial for reducing solidification defects. In this study, a multi-phase-field lattice Boltzmann (MPF-LB) model, which can simulate growth of multiple dendrites with liquid flow, solid motion and collision, is applied to semi-solid deformation. An elastic contact is introduced to the MPF-LB model to conside...

In this study, two-dimensional large-scale simulation of polycrystalline equiaxed solidification is enabled by applying an active parameter tracking and multiple GPUs computation to the phase-field lattice Boltzmann model, which can simulate growth of multiple dendrites with solid motion, liquid flow, collision and coalescence of multiple solids, a...

Solid-liquid interfacial properties out of equilibrium provide the essential information required for understanding and controlling solidification microstructures in metallic materials. However, few studies have attempted to reveal all interfacial properties out of equilibrium in detail. The present study proposes an approach for simultaneously est...

Permeability is a very important multiscale parameter providing information of dendritic structures in macroscale simulations of solidification with liquid flow during casting. In our previous study, it was demonstrated that the permeability of liquid flow normal to a columnar dendritic structure can be well approximated by the Kozeny–Carman (KC) e...

The effects of natural convection on dendrite morphologies formed during solidification of a three–dimensional (3D) bulk crystal have not been clarified yet. Although numerical simulation is key to solve the problem, it is not straightforward from a computational cost point of view to simulate the growth of multiple dendrites and liquid flow simult...

In solidification of metals and alloys under earth's gravity, the growing free equiaxed dendrites either settle or float because of the difference between the solid and liquid densities. In this study, we developed a two-dimensional computational method that can efficiently simulate the growth of free dendrite settling over a long distance. In the...

Morphological change of equiaxed dendritic structure in fcc-based alloys associated with transition in preferred growth direction was investigated by means of three-dimensional quantitative phase-field simulations. The anisotropy parameters of interfacial energy ε1 and ε2 were systematically changed to investigate the growth direction and growth mo...

In this study, assuming an ideal system free from thermal grooving and anisotropy in grain boundary properties, we analyze thin-film grain growth via three-dimensional (3D) phase-field simulations with approximately one million initial grains. The large-scale simulations accelerated by multiple graphics processing units allow for the reliable stati...

The micrometer-scale polycrystalline microstructure is directly obtained from a 10 billion atom molecular dynamics (MD) simulation of the nucleation and growth of crystals from an undercooled melt, which is performed on a graphics processing unit-rich supercomputer. The grain size distribution in the as-grown microstructure obtained from the MD sim...

In this study, an adaptive mesh refinement (AMR) method is applied to phase-field lattice Boltzmann simulation of the dendrite growth with liquid flow and solid motion. Furthermore, a parallel computation using multiple graphics processing units (GPUs) is implemented for the method. To evaluate computational efficiency of the multi-GPUs AMR method,...

A lot of numerical studies have so far been conducted to systematically investigate the effects of anisotropic grain boundary properties on grain growth. Nevertheless, conclusive knowledge on the correlations between boundary properties and grain growth characteristics is not yet established, which is mainly due to insufficient statistics coming fr...

In actual solidification of alloys, multiple equiaxed dendrites grow with motion. In our previous study, the phase-field lattice Boltzmann method (PF-LBM) that can simulate formation process of equiaxed structure by considering growth, motion, collision, and coalescence of multiple dendrites, was developed, where double-well potential was employed...

Grain growth is one of the most fundamental phenomena affecting the microstructure of polycrystalline materials. In experimental studies, three-dimensional (3D) grain growth is usually investigated by examining two-dimensional (2D) cross sections. However, the extent to which the 3D microstructural characteristics can be obtained from cross-section...

Computer simulation is the most promising approach for the systematical permeability prediction of liquid flow in the mushy zone for various solidification conditions. In this study, we propose a permeability prediction method by using large–scale simulation of phase–field and lattice Boltzmann methods. Using the proposed method, permeability predi...

Competitive grain growth during the directional solidification of a polycrystalline binary alloy is investigated by performing systematic three-dimensional large-scale phase-field simulations with the GPU supercomputer TSUBAME2.5 at the Tokyo Institute of Technology. Contrary to two-dimensional investigations, in which an unusual growth of unfavora...

Grain growth kinetics under the anisotropic grain boundary properties is investigated by large-scale and long-time molecular dynamics (MD) simulations of contentious processes of nucleation, solidification and grain growth in a submicrometer-scale system. Microstructures obtained via homogeneous nucleation from undercooled melt iron consists of app...

Dendrite fragmentation is one of the most remarkable phenomena in solidification of alloys, because it would be potential nuclei of equiaxed structure. However, the mechanism of dendrite fragmentation is not clarified yet. In this study, a numerical model, which can simulate the dendrite fragmentation and following flow of a fragmented part, is dev...

In this study, the adaptive mesh refinement (AMR) method is applied to a phase-field dendrite growth simulation using a graphic processing unit (GPU). To evaluate a computational efficiency of the implemented AMR method, dendrite growth simulations during directional solidification with and without AMR are performed. From simulation results, we con...

Permeability tensor of mushy region is very important to accurately predict macrosegregation in casting. In this study, we investigate the permeability changes in a plane normal to a columnar dendrite by employing phase-field and lattice Boltzmann methods. As a result, it is concluded that a two-dimensional permeability tensor with coordinate trans...

Can completely homogeneous nucleation occur? Large scale molecular dynamics simulations performed on a graphics-processing-unit rich supercomputer can shed light on this long-standing issue. Here, a billion-atom molecular dynamics simulation of homogeneous nucleation from an undercooled iron melt reveals that some satellite-like small grains surrou...

Three-dimensional growth morphologies of equiaxed dendrites growing under forced convection, with their preferred growth direction inclined from the flow direction, were investigated by performing large-scale phase-field lattice Boltzmann simulations on a graphical-processing-unit supercomputer. The tip velocities of the dendrite arms with their pr...

Grain growth, a competitive growth of crystal grains accompanied by curvature-driven boundary migration, is one of the most fundamental phenomena in the context of metallurgy and other scientific disciplines. However, the true picture of grain growth is still controversial, even for the simplest (or ‘ideal’) case. This problem can be addressed only...

Melt flow drastically changes dendrite morphology during the solidification of pure metals and alloys. Numerical simulation of dendrite growth in the presence of the melt flow is crucial for the accurate prediction and control of the solidification microstructure. However, accurate simulations are difficult because of the large computational costs...

Simulating dendritic growth with natural convection is challenging because of the size of the computational domain required when compared to the dendrite scale. In this study, a phase-field-lattice Boltzmann model was used to simulate dendritic growth in the presence of natural convection due to a difference in solute concentration. To facilitate a...

Continuous processes of homogeneous nucleation, solidification and grain growth are spontaneously achieved from an undercooled iron melt without any phenomenological parameter in the molecular dynamics (MD) simulation with 12 million atoms. The nucleation rate at the critical temperature is directly estimated from the atomistic configuration by clu...

Primary arm arrays formed during the directional solidification of a single-crystal binary alloy were investigated by performing large-scale phase-field simulations using the GPU supercomputer TSUBAME2.5 at Tokyo Institute of Technology. The primary arm array and spacing were investigated by Voronoi decomposition and Delaunay triangulation, respect...

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 th...

Nucleation and solidification from the undercooled iron melt are investigated from the atomistic point of view by large-scale molecular dynamics (MD) simulations up to 12 million atoms in systems of the submicrometer-scale. There exist some amount of atoms with icosahedral configuration in the undercooled iron melt and these atoms increase with dec...

Selections of growing crystals during directional solidification of a polycrystalline binary alloy were numerically investigated using two-dimensional phase-field simulations. To accelerate the simulations, parallel graphics processing unit (GPU) simulations were performed using the GPU-rich supercomputer TSUBAME2.5 at the Tokyo Institute of Techno...

Phase-field method has emerged as the most powerful numerical scheme to simulate dendrite growth. However, most phase-field simulations of dendrite growth performed so far are limited to two-dimension or single dendrite in three-dimension because of the large computational cost involved. To express actual solidification microstructures, multiple de...