Integrated modelling and simulation of NiTi alloy by powder bed fusion: Single track study

Abstract

In-depth understanding of the layer-by-layer process is critical for the quality control of additive manufactured (AM) components. Besides the development of experimental techniques, computational modelling is another important way to study the AM mechanisms in detail. However, currently there is still lack of a modelling platform that integrates all the necessary physics involved in the AM process. In the present study, we develop a modelling framework that integrates a phase field method for microstructure evolution, a lattice Boltzmann method for melt pool dynamics, a modified ray-tracing method for laser-material interaction, and a minimum gravity energy algorithm for powder bed generation to simulate the single-track, powder bed fusion (PBF) process of NiTi shape memory alloy. Our simulation shows that different from keyhole depth, melt pool size does not obey the scaling law with line energy density, the keyhole depth and the overlapping ratio of laser spot vs. keyhole opening together determine the laser absorptivity. Based on the simulation finding, we also develop a self-consistent analytical model to predict the keyhole depth and the absorptivity for given scanning parameters. The present work lays a solid foundation towards quantitative understanding of multi-layer AM process.

Keywords

• Additive manufacturing
• Phase field simulation
• Lattice Boltzmann method
• NiTi shape memory alloy