On multi-scale modelling of dendrite growth during laser metal deposition process

A numerical study of the influence of macroscopic processes of heat and mass transfer on the dendrites formation during laser metal deposition is carried out in the paper. The algorithm used to calculate the processes realizes the concept of multiscale modeling of crystallization and provides the interaction of models of different structural levels. Simulation of macro-level processes is carried out on the basis of 3D self-consistent equations for the dynamics of the free surface, temperature, and melt flow velocities. The microlevel problems are related to the modeling of the formation of dendrites during the crystallization of the melt and are solved using the phase field equation conjugate with the of heat conduction equation. The profiles of the phase field and the temperature gradient in different spatial regions of the object being formed are calculated. The orientation of the dendritic structures strongly depends on the thermal prehistory and the shape of the melt pool and varies in different areas. In the near-surface layers, the dendrites have a pronounced orientation along the plane of the part. In the process of depositing the material over the previously treated areas, the microstructural properties of the crystallized material change partially. After solidification in areas that have undergone repeated remelting, dendrites oriented vertically appear. With the growth of the temperature gradient, the morphology of the dendrites transforms with the formation of columnar structures.