SIMULATION OF NUCLEATION AND GRAIN GROWTH IN SELECTIVE LASER MELTING OF TI-6AL-4V ALLOY

Selective laser melting (SLM) builds parts by selectively melting metallic powders layer by layer with a high-energy laser beam. It has a variety of applications in aerospace, medical device, and other low-volume manufacturing. Nevertheless, the lack of fundamental understanding of the process -structureproperty (P-S-P) relationship for better quality control inhibits wider applications of SLM. Recently, a mesoscale simulation approach, called phase-field and thermal lattice Boltzmann method (PF-TLBM), was developed to simulate microstructure evolution of alloys in SLM melt pool with simultaneous consideration ofsolute transport, heat transfer, phase transition, and latent heat effect. In this paper, a nucleation model is introduced in the PF-TLBM model to simulate heterogeneous nucleation at the boundary of melt pool in SLM. A new method is also developed to estimate the thermalflux out ofthe SLM melt pool model given a constant cooling rate. The effects of latent heat and cooling rate on dendritic morphology and solute distribution are studied. The simulation results of Ti-6A1-4V alloy suggest that the inclusion of latent heat is necessary because it reveals the details oftheformation ofsecondary arms, reduces overestimated microsegregation, and provides more accurate kinetics ofdendritic growth.