Multi-scale phase-field modeling of layer-by-layer powder compact densification during solid-state direct metal laser sintering

Solid-state direct metal laser sintering (S-DMLS) builds structures by using laser energy to sinter powder particles in a layer-by-layer manner. Powder size distribution (PSD) is an important parameter governing the densification of powders and the overall quality of as-built S-DMLS parts. Therefore, this work aims to reveal the underlying mechanism of layer-by-layer powder compact densification during the S-DMLS with different PSDs via a multi-scale computational framework: 1) a powder-based 3D heat transfer simulation is conducted to predict the thermal response at the macroscale during laser heating; 2) the obtained thermal information is input to a non-isothermal phase-field model to simulate the sintering behavior of powder particles in a layer-by-layer manner at the mesoscale. Using stainless steel 316 Las an example, a narrow PSD presents a small volume of gap between powders with an elevated effective thermal conductivity, causing a deep laser-induced heating zone that promotes full grain coalescence and reduces porosity during the S-DMLS. Furthermore, a bimodal powder mixture with an optimized size ratio can also effectively reduce the porosity of as-built S-DMLS parts. Moreover, the effect of layer-wise manufacturing on the densification is comprehensively explored. Finally, the influences of laser beam size and scanning speed are discussed. (c) 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This study revealed the mechanisms of layer-by-layer powder compact densification during S-DMLS with different PSDs using a multi-scale computational framework. The impact of layer-wise manufacturing on densification, as well as the influences of laser beam size and scanning speed, were comprehensively explored.