Effect of magnetic field on interfacial instabilities of rapid solidification in additive manufacturing

Abstract

The performance of additive manufacturing products is significantly influenced by the microstructural morphology developed during rapid solidification, where instability at the solid–liquid interface can result in various microstructural modes. The application of a magnetic field to modify the hydrodynamic mechanism within a molten pool presents a promising approach to controlling the microstructure evolution in additive manufacturing. This study establishes a mathematical and physical model of rapid directional solidification and investigates the impact of the magnetic field on the stability of the solidification interface through linear stability analysis. The results show that an external magnetic field decreases both the maximum and cutoff wave numbers in the steady mode, delaying the onset of instability. Furthermore, the extent of the unstable region in the steady mode diminishes as the Hartmann number increases. In the oscillatory mode, the application of the magnetic field increases the maximum and cutoff wave numbers, thereby promoting interfacial instabilities. However, the magnetic effect on the unstable region is not remarkable. Utilizing dimensionless drag velocity as a control parameter for rapid solidification reveals that the magnetic field can reduce the cell/dendrite domain and the solute banding region, thereby enhancing interfacial stability. The enhancement can be understood as a result of the external magnetic field promoting melt flow, with the associated stirring effect leading to increased supercooling and solidification rates, ultimately improving structural uniformity. The conclusions provide some theoretical guidance for utilizing the magnetic field to reduce defects and enhance high-quality products in additive manufacturing, potentially paving the way for further experimental investigations.