Abstract Fragmentation of solid grains is known to occur readily when external forces are applied to metals in the semi-solid state. In this study, to clarify the underlying mechanism of this fragmentation, molecular dynamics simulations of semi-solid deformation are performed, in which a single-crystal solid grain embedded in liquid is compressed by a rigid plate. The results indicate that stress concentration induces local melting, which plays a key role in triggering fragmentation.
Abstract A 3D sequentially coupled heat-transfer–Cellular Automaton model is used to investigate grain structure evolution during Laser Powder Bed Fusion with laser rescanning (LPBF-LR) of Al–10Si. Starting from a fixed first scan (130 W, 0.2 m/s), we systematically vary (i) rescanning power and speed, (ii) scanning strategies, (iii) scanning length with alternating reversal, and (iv) rescanning rotations to evaluate their effects on microstructure. Grain geometry is quantified using Principal Component Analysis, and texture is assessed through simulated pole figures. Reduced power and higher speed promote grain refinement by shallowing the melt pool and modifying the local thermal conditions (G/v and cooling rate). Among the strategies, an island-type pattern produces the strongest refinement due to localized reheating and overlapping melt pools, which expand equiaxed zones. Rotation angle has minimal influence on grain size in single-layer LR but systematically rotates the dominant <100> texture, indicating a potential route for texture homogenization in multi-layer builds.
Abstract Traditional thermal analysis such as differential thermal analysis (DTA) and differential scanning calorimetry (DSC) is typically constrained to cooling rates lower than 30°C/min. To study solidification at faster cooling rates, an improved technique was developed coupling a high-temperature infrared furnace with a thermal imaging camera (TIC) to analytically determine the onset temperatures for solidification and δ→γ transformation at cooling rates between 120 to 600°C/min. A heat-transfer and solidification model was developed to predict and help interpret the resulting thermal curves. The model was calibrated using the melting and freezing of pure Fe.
Abstract During directional solidification, the misorientation of dendrites is often identified as a potential cause of various unwanted microstructural features. However, the precise physical mechanisms driving this and how this impacts the transient morphological development of the dendrites remain under-explored and poorly understood. One phenomenon often posited for this is the impact of fluid flow in the melt, such as may occur from solute buoyancy or magnetic stirring. This paper presents initial results from the coupling of existing solvers for dendritic solidification, fluid flow, and structural mechanics, allowing a close examination of the transient morphological development of a dendrite under different conditions. This has served to highlight a potential mechanism in which the preferential growth behaviour induced by fluid flow leads to a smaller misorientation than would be suggested by resolving structural mechanics independently.
Abstract Solid fragmentation during solidification contributes to microstructural refinement, but its underlying mechanisms remain incompletely understood due to the complex interplay of multi-physical phenomena. In this study, a multi-physics model coupling the phase-field method, the lattice Boltzmann method, and the material point method is applied to simulate uniaxial compression of dendritic and granular structures between two rigid plates, with solid–solid contact interactions taken into account, to examine the effect of microstructural morphology on fragmentation behavior. The results show that, in dendritic structures, bending deformation induces stress concentration and significant lattice rotation, promoting grain boundary formation and the onset of behavior associated with fragmentation. In contrast, the granular structure exhibited distinct deformation behavior characterized by limited lattice rotation, and grain boundary formation and fragmentation were not reproduced under the present conditions. These findings highlight that deformation behavior strongly depends on microstructural morphology.
