Finite Interface Dissipation Phase Field Modeling of Ni-Nb under Additive Manufacturing Conditions

During laser powder bed fusion (L-PBF) parts undergo multiple rapid heating-cooling cycles, leading to complex microstructures with nonuniform properties. In the present work, a computational framework which weakly couples a finite element thermal model to a non-equilibrium PF model was developed to investigate the rapid solidification microstructure of a Ni–Nb alloy during L-PBF. The framework is utilized to predict the spatial variation of the morphology and size of cellular segregation structures as well as the differences in melt pool microstructures obtained under different process conditions. A solidification map demonstrating the variation of microstructural features as a function of the temperature gradient and growth rate is presented. A planar to cellular transition is predicted in the majority of keyhole mode melt pools, while a planar interface is predominant in conduction mode melt pools. The predicted morphology and size of the cellular segregation structure agree well with experimental measurements.