PSI - Issue 69

Mohammadjavad Abdollahzadeh et al. / Procedia Structural Integrity 69 (2025) 2–19

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capability concerning the impact of hatch distance on the grain morphology of Nickel-Titanium (NiTi) alloys [26]. Chen et al. focused on NiTi, demonstrating that elevating the combination of laser power and scan speed rendered the melt pool shallower, yet expanded the region of highest temperature [27]. While some studies have indeed engaged Nickel Titanium (NiTi) as the focal material [25-27, 51], their methodologies have predominantly utilized finite element or analytical techniques combined coupled with experimental modeling. Notably, a significant gap persists in the literature, marked by a few of investigations dedicated to examining the fluid dynamics within the melt pool during the LPBF process of NiTi alloys. Given the crucial role fluid flow plays in melt pool formation and solidification, neglecting this aspect can inadvertently limit a comprehensive understanding of the process dynamics and, by extension, the properties of the resulting material. Therefore, the incorporation of melt pool fluid dynamics in NiTi based LPBF studies can improve the modeling accuracy, consequently enhancing our insight into the LPBF process, the resulting material behavior, and the overall part quality. While prior studies on NiTi LPBF have primarily focused on analytical modeling or finite element approaches, they often lack detailed insight into fluid flow phenomena, particularly the role of melt pool dynamics in defect formation. Moreover, few models incorporate realistic powder bed generation or temperature-dependent material properties derived from thermodynamic databases. This study addresses these gaps by employing an integrated, physics-informed simulation approach to capture melt pool behavior in NiTi under LPBF conditions, providing a more comprehensive and accurate representation of the process. In light of this, the present research aims to develop a three-dimensional model for predicting the thermo-physical properties, flow mechanisms within the melt pool, and the morphological attributes of melted tracks during the LPBF process of NiTi materials. The DEM is used to construct a 3D powder bed with randomly distributed spherical particles, closely mimicking real-world manufacturing conditions. Thermo-Calc software is employed to predict the temperature-dependent material properties, such as thermal conductivity, viscosity, and surface tension, which are then incorporated into the CFD model. CFD simulations are carried out using the Flow3D package to analyze fluid flow and heat transfer within the melt pool, providing insights into the interplay of thermal and dynamic processes. Additionally, the effects of various process parameters on melt pool dynamics are systematically evaluated. The agreement between the model’s predictions and experimental results confirms its accuracy and reliability, demonstrating its potential as a powerful tool for understanding and optimizing the LPBF process for NiTi materials.

2. Modeling Approach 2.1. Powder Bed Generation

In this research, the powder bed was generated through a two-step process to simulate realistic LPBF conditions. First, NiTi powder particles were poured vertically onto a substrate to form a mound. Then, a blade or roller spread the particles across the surface at a velocity of 0.05 cm/s, creating a uniform layer. The powder bed was modeled using the DEM package in Flow3D-AM. To enhance realism, particles were distributed randomly, with diameters ranging from 20 to 30 μm. A normal distribution of particle sizes was achieved by including five sizes: 20 μm (10%), 22.5 μm (15%), 25 μm (50%), 27.5 μm (15%), and 30 μm (10%). The computational cell size was set to 0.003 cm, providing high resolution, and the particle density was defined as 6.452 g/cm³. Powder bed generation steps in this research are shown in Figure 1.