Multiphysics Modeling of NiTi Shape Memory Alloy Fabricated by Laser Powder Bed Fusion Using Computational Fluid Dynamics

Laser Powder Bed Fusion (LPBF) is a transformative additive manufacturing technique capable of producing high-performance components with intricate geometries. This study focuses on the LPBF of NiTi alloys. Material properties were predicted using Thermo-Calc (V-2022a), employing the ‘Scheil Solidification simulation’ and ‘property model calculation’ to account for time-dependent thermal and physical behavior during processing. These properties were integrated into a Computational Fluid Dynamics (CFD) model to analyze the morphology of the melt pool, as well as the dynamic fluid flow, heat transfer, and key phenomena such as Marangoni convection, recoil pressure, and defect formation under realistic conditions. The powder bed was simulated using the Discrete Element Method (DEM) to replicate the random particle distribution typical of real-world LPBF processes. The results, validated against experimental data with an error of ~15%, revealed relationships between energy density, melt pool morphology, and defect formation. Key phenomena such as Marangoni convection, recoil pressure, and Rayleigh instability were identified as primary factors influencing melt pool behavior. The temporal evolution of the melt pool highlighted the role of thermal gradients and laser penetration depth in achieving uniform fusion. This study provides insights into LPBF melt pool physics and process optimization, offering a framework for the reliable fabrication of high-quality NiTi components. These findings have significant implications for advancing applications in various industries.