Fluid Dynamics Effects on Microstructure Prediction in Single-Laser Tracks for Additive Manufacturing of IN625

Abstract

Abstract Single-track laser fusion were simulated using a heat-transfer-solidification-only (HTS) model and its extension with fluid dynamics (HTS_FD) model using a parallel open-source code, which included laminar fluid dynamics, flat-free surface of the molten alloy, heat transfer, phase-change, evaporation, and surface tension phenomena. The results illustrate that the fluid dynamics affects the solidification and ensuing microstructure. For the HTS_FD simulations, thermal gradient, G was found to exhibit a maximum at the extremity of the solidified pool ( i.e. , at the free surface), while for HTS simulations, G exhibited a maximum around the entire edge of the solidified pool. HTS_FD simulations predicted a wider range of cooling rates than the HTS simulations, exhibited an increased spread in the solidification speed, V variation within the melt-pool with respect to the HTS model results. Primary dendrite arm spacing (PDAS) were evaluated based on power law correlations and marginal stability theory models using the ( G , V ) from HTS and HTS_FD simulations to quantify the effect of the fluid dynamics on the microstructure. At low-laser powers and low-scan speeds, the PDAS obtained with the fluid dynamics model (HTS_FD) was larger by more than 30 pct with respect to the PDAS calculated with the simple HTS model. A new PDAS correlation, i.e. , $$ \lambda_{1} \left[ {\mu {\text{m}}} \right] = 832\;G\left[ {\text{K/m}} \right]^{ - 0.5} V\left[ {\text{m/s}} \right]^{ - 0.25} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>λ</mml:mi> <mml:mn>1</mml:mn> </mml:msub> <mml:mfenced> <mml:mrow> <mml:mi>μ</mml:mi> <mml:mtext>m</mml:mtext> </mml:mrow> </mml:mfenced> <mml:mo>=</mml:mo> <mml:mn>832</mml:mn> <mml:mspace/> <mml:mi>G</mml:mi> <mml:msup> <mml:mfenced> <mml:mtext>K/m</mml:mtext> </mml:mfenced> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>0.5</mml:mn> </mml:mrow> </mml:msup> <mml:mi>V</mml:mi> <mml:msup> <mml:mfenced> <mml:mtext>m/s</mml:mtext> </mml:mfenced> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>0.25</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> , which uses the ( G , V ) results from the HTS_FD model was developed and validated against experimental results.