On the choice of thermal boundary conditions for microstructure modelling of additive processes

Abstract

Advanced phase-field modelling of LPBF should consider both melting and solidification, because microstructure quantities like the primary dendrite spacing as well as grain orientations typically are inherited across successive layers. This cannot be achieved by considering constant cooling conditions, which however still is state of the art by now. In this work, two different types of thermal boundary conditions that both allow taking the transition between melting and solidification into account have been implemented and compared. For a given set of laser process parameters, the melting and solidification dynamics, melting depth, dendritic microstructure and grain selection have been simulated in 2d for the multicomponent Ni-base alloy ABD®-900AM. It is demonstrated that latent heat release has a significant impact on the thermal conditions at the dendrite tips, and thus on microstructure. The simulation results are discussed by comparison with analytical heat source models, heat balance considerations and experimental results.