Prediction of 3D microstructure and phase distributions of Ti6Al4V built by the directed energy deposition process via combined multi-physics models

In this paper, a multiphysics and multiscale integrated simulation framework is established to link the thermal history with the microstructural evolution and resulting properties of Ti6Al4V in additive manufacturing processes by combining: (1) a three-dimensional (3D) multiphysics modeling of quasi-steady-state deposition geometry and thermal history in the directed energy deposition (DED) process, (2) a 3D cellular automata modeling of the solidification grain structure, and (3) a diffusion/diffusionless kinetic modeling of solid-state phase transformation and microhardness prediction based on the simulated phase volume fractions. By applying to Ti6Al4V, this integrated simulation framework demonstrates its feasibility in modeling complex microstructural evolution and phase transformation during the multi-track DED process. The simulated track geometry and thermal history agree well with experimental results. Coupled with the extracted temperature profiles and heating/cooling rates, the competitive growth of beta grains upon solidification of the molten pool is successfully predicted. The solid-state beta ->alpha/alpha' transformation in the fusion zone and heat-affected zone is then captured by the kinetic solid-state phase prediction model. With the predicted volume fractions of alpha and alpha' in the final microstructure, the microhardness is assessed, matching the experimental measurements.