Session: 12-21-01: Multiphase Flow

Paper Number: 164543

The Effects of Process Parameters on Nanoparticle Distribution and Microstructure Formation During Selective Laser Melting 

Selective laser melting (SLM) is a widely used metal additive manufacturing process for fabricating metal matrix nanocomposites by fusing metallic powders with nanoparticles. However, the complex fluid dynamics of the molten pool flow, generated by a moving laser heat source, redistributes nanoparticles when process parameters such as laser scanning speed, laser power, and preheating temperatures are varied. Consequently, the microstructures of the solidified molten pool are influenced by the local nanoparticle distribution. Nanoparticles can act as nucleation sites, disrupting growth of large columnar grains and promoting the growth of smaller grains. As the average grain size decreases, mechanical properties such as mechanical strength, hardness etc. increase. In this study, we employed a novel numerical model to simulate the microstructure formation of AlSi10Mg alloy, considering reinforced TiB₂ nanoparticle distribution for a single track and single scan SLM process. This model couples a computational fluid dynamics (CFD) model with a Cellular Automata (CA) microstructure model. The boundary and load conditions, used in this model along with the coupling algorithm and its validation with experimentally published results are described in our previous works. In the current study, we have conducted a parametric analysis to investigate the effects of laser power, laser scanning speed, and preheating temperature on nanoparticle distribution dynamics and microstructure evolution. Our results indicate that decreasing laser scanning speed and increasing laser power results in increased energy absorption by the powder, raising the maximum surface temperature and volume of the molten pool. This intensified Marangoni convection generates a dynamic recirculation zone along the laser direction and the perpendicular plane. In these zones, nanoparticles are pushed outward by centrifugal force, leading to pronounced void regions under high energy density conditions. Due to the absence of nanoparticles, grain nucleation of the undercooled liquid was restricted in the voided regions, resulting in a local increase in grain sizes in these areas. In addition, the simulated microstructure showed the presence of small grains where nanoparticles were uniformly distributed. Conversely, higher scanning speeds and lower laser power yielded more uniform nanoparticle distribution, albeit with a smaller molten pool volume. A uniform nanoparticle distribution promotes more grain nucleation sites and contributes to a smaller average grain diameter. Finally, elevated preheating temperatures expanded molten pool dimensions with less impact on maximum temperature. Despite larger molten pool dimensions, Marangoni convection remains low, resulting in fewer void regions. Therefore, a smaller increase in average grain sizes is observed even at high preheating temperatures.

Presenting Author: M. Ruhul Amin Montana State Univ

Presenting Author Biography: M. Ruhul Amin has received the Ph.D. degree in mechanical engineering from the University of Tennessee, USA. He is a professor of mechanical engineering at Montana State University, USA with extensive background in computational heat transfer and fluid flow. He is the program coordinator of mechanical engineering program at Montana State University and an ABET Program Evaluator. Dr. Amin is a Fulbright Scholar, a member of ASME, and member of ASME technical committees. He is a registered professional engineer in the State of Montana. He has chaired and co-chaired numerous technical sessions at international technical conferences. He also co-chaired several international conferences on thermal sciences.

Authors:

Taosif Alam The Ohio State University
M. Ruhul Amin Montana State Univ