Microscopic scale analysis of the dynamic changes of the melt pool and the evolution of dendritic structure during L-DED of GH3536 alloy

This paper presents the establishment of a melt pool flow model, wherein the solute field and phase field are concurrently integrated to simulate the dynamic transformations within the melt pool and the evolution of dendrites during the solidification process. Experimental validation affirms the model's precision. The simulation outcomes indicate the persistence of a pronounced symmetry within the melt pool throughout the flow process. Intriguingly, perturbations in the powder and variations in heat transfer give rise to a vortex-like internal flow pattern within the melt pool. These findings align harmoniously with the experimental results concerning the dimensions of the melt pool (melt width, melt depth, and melt height). Specifically, the growth rate of dendrite tips and the dendrite count exhibit significant sensitivity to alterations in temperature gradient. As the temperature gradient escalates, the primary dendrite arm spacing diminishes, accompanied by heightened development of secondary dendrite arms. In congruence with the simulated dendrite evolution process, the microstructure within the deposited layer derived from experimental observations primarily comprises columnar crystals. The growth of dendrites unfolds perpendicularly to the melt pool boundary, following the trajectory of decreasing temperature gradient, thereby mirroring the simulated dendrite evolution process.