Development of the molten pool and solidification characterization in single bead multilayer direct energy deposition

Abstract

Although single-layer directed energy deposition has been extensively studied, an in-depth understanding of the cladding melting and solidification mechanism of single bead multilayer directed energy deposition is equally promising for industry, considering practical application scenarios. Based on the single-layer directed energy deposition, a numerical model of multilayer directed energy deposition was developed and validated to reveal the cladding forming process and solidification structure of multilayer directed energy deposition. The simulation results show the complex Marangoni convection pattern generated by the surface tension gradient in the melt pool. Moreover, the multilayer directed energy deposition enhances the penetration effect of the melt pool under the influence of the heat accumulation effect, resulting in a cross-layer mass transfer different from that of the single-layer directed energy deposition. The evolution of the multilayer cladding from columnar crystals at the bottom to equiaxed crystals at the top and the shift of its growth orientation were also analyzed based on the obtained solid-liquid interface temperature gradients and solidification velocities during the solidification of the melt pool. Finally, the relationship between cladding grain size and solidification properties was theoretically predicted by counting the grain size of different layers in the cladding, and the effect of grain growth on the mechanical properties was superficially discussed. • Penetration of multilayer deposition melt pools enhanced by heat accumulation effects. • Cross-layer mass transfer exists for multilayer deposition. • "C" or "U" type of grain growth orientation transition. • The recrystallization after solidification promotes the mechanical properties.