Multi-scale Simulation of Dendritic Growth in Laser-Melted Alumina

The present study employs a two-scale modeling approach to study the evolution of columnar (dendrite) structures during laser melting and solidification in alumina. The framework, which combines the finite element and phase-field methods, is used to simulate temperature evolution and melt pool characteristics at the macroscale and the growth of dendritic structures at the microscale. The model reveals the relationships between process parameters and microstructure morphology in laser-melted alumina by examining the effects of laser parameters on cooling rates, thermal gradient, solidification speed, and dendritic growth. The findings from the numerical simulations are validated against experimental data from previous works. It is found that the melt pool exhibits a double ellipsoidal shape during laser heating. The cooling rates and solidification speed decrease with the depth and increase with the scan speed, whereas the thermal gradient takes the opposite trend. The solidification structures exhibit three growth stages: planar, cellular, and dendritic growth regimes, with two transition periods. The primary dendritic arm spacing, growth direction, growth rate, and tip radius strongly depend on the laser heating parameters and misorientation angle due to changes in capillary forces. Inclined growth direction and complex microstructure with local side branches are observed at high misorientation angles. This work could lead to the development of a powerful simulation module for optimizing laser processing windows and enhancing the mechanical properties, thermal stability, and durability of alumina, paving the way for improved laser processing methods in ceramic manufacturing.