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;Gleft[ {text{K/m}} right]^{ - 0.5} Vleft[ {text{m/s}} right]^{ - 0.25} , which uses the (G, V) results from the HTS_FD model was developed and validated against experimental results.
Highlights
ADDITIVE manufacturing (AM) is a revolutionary manufacturing process with clear advantages such as lower energy usage, minimum scrap waste, lower buy-to-fly ratio and shorter lead time to market.[1]
As a step toward a comprehensive multi-physics laser powder-bed fusion additive manufacturing (LPBF) model, single-track laser fusion (STLF) simulations were conducted for the nickel-base superalloy (IN625) assuming a flat-free surface of the molten alloy
For the fluid dynamics (HTS_FD) model (Figures 5(b), (d), and (f)), G was found to exhibit a maximum at the extremity of the solidified pool and the minimum in the central region below the free surface of the solidified pool
Summary
ADDITIVE manufacturing (AM) is a revolutionary manufacturing process with clear advantages such as lower energy usage, minimum scrap waste, lower buy-to-fly ratio and shorter lead time to market.[1]. Truchas, is an open-source massively parallel CFD software that was developed under the Advanced Simulation and Computing (ASC) program at Los Alamos National Laboratory (LANL) for the simulation of metal-casting processes.[16] Truchas has been used to simulate the heat transfer and solidification of electron beam additive manufacturing process[17,18,19,20] without including fluid dynamics effects. As a step toward a comprehensive multi-physics LPBF model, single-track laser fusion (STLF) simulations were conducted for the nickel-base superalloy (IN625) assuming a flat-free surface of the molten alloy. This assumption is expected to underpredict the meltpool depth for IN625 (which has negative surface tension coefficient),[26] important insights can be obtained on the effect of fluid flow on the solidification during LPBF. The variation of the microstructure-related variables, G, V, G/V, and GV over the solidified melt-pool was assessed, to understand the microstructure variation in LPBF process
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