Numerical modeling of the dispersion of ceramic nanoparticles during ultrasonic processing of aluminum-based nanocomposites

AbstractThe metal–matrix-nano-composites (MMNCs) in this study consist of a 6061 alloy matrix reinforced with 1.0wt.% SiC nanoparticles that are dispersed within the matrix using an ultrasonic cavitation dispersion technique available in the Solidification Laboratory at the University of Alabama.The required ultrasonic parameters to achieve (i) the required stirring and cavitation for suitable degassing and refining of the aluminum alloy and (ii) the adequate fluid flow characteristics for uniform dispersion of the nanoparticles into the 6061 matrix are being investigated in this study by using an in-house developed CFD ultrasonic cavitation model. The multiphase CFD model accounts for turbulent fluid flow, heat transfer, and the complex interaction between the molten alloy and nanoparticles by using the ANSYS's Fluent DDPM.The modeling parametric study includes the effects of the fluid flow, the ultrasonic probe location, nanoparticle size distribution, and initial location where the nanoparticles are released into the molten alloy. It was determined that the nanoparticles can be distributed quickly and uniformly into the molten 6061 alloy

3D Modeling of the Solidification Structure Evolution and of the Inter Layer/Track Voids Formation in Metallic Alloys Processed by Powder Bed Fusion Additive Manufacturing

A fully transient discrete-source 3D Additive Manufacturing (AM) process model was coupled with a 3D stochastic solidification structure model to simulate the grain structure evolution quickly and efficiently in metallic alloys processed through Electron Beam Powder Bed Fusion (EBPBF) and Laser Powder Bed Fusion (LPBF) processes. The stochastic model was adapted to rapid solidification conditions of multicomponent alloys processed via multi-layer multi-track AM processes. The capabilities of the coupled model include studying the effects of process parameters (power input, speed, beam shape) and part geometry on solidification conditions and their impact on the resulting solidification structure and on the formation of inter layer/track voids. The multi-scale model assumes that the complex combination of the crystallographic requirements, isomorphism, epitaxy, changing direction of the melt pool motion and thermal gradient direction will produce the observed texture and grain morphology. Thus, grain size, morphology, and crystallographic orientation can be assessed, and the model can assist in achieving better control of the solidification microstructures and to establish trends in the solidification behavior in AM components. The coupled model was previously validated against single-layer laser remelting IN625 experiments performed and analyzed at National Institute of Standards and Technology (NIST) using LPBF systems. In this study, the model was applied to predict the solidification structure and inter layer/track voids formation in IN718 alloys processed by LPBF processes. This 3D modeling approach can also be used to predict the solidification structure of Ti-based alloys processes by EBPBF

3D Modeling of the Solidification Structure Evolution of Superalloys in Powder Bed Fusion Additive Manufacturing Processes

Recently, a few computational methodologies and algorithms have been developed to simulate the microstructure evolution in powder bed fusion (PBF) additive manufacturing (AM) processes. However, none of these have attempted to simulate the grain structure evolution in multitrack, multilayer AM components in a fully 3D transient mode and for the entire AM geometry. In this work, a multiscale model, which consists of coupling a transient, discrete-source 3D AM process model with a 3D stochastic solidification structure model, was applied to quickly, efficiently, and accurately predict the grain structure evolution of IN625 alloys during Laser Powder Bed Fusion (LPBF). The capabilities of this model include studying the effects of process parameters and part geometry on solidification conditions and their impact on the grain structure formation within multicomponent alloy parts processed via AM. Validation was accomplished based on single-layer LPBF IN625 benchmark experiments, previously performed and analyzed at the National Institute of Standards and Technology (NIST), USA. This modeling approach can also be used to quantitatively predict the solidification structure of Ti-6Al-4V alloys in electron beam AM processes

Numerical modeling of fluid flow and solidification phenomena during ultrasonic processing of metal-matrix-nanocomposites

In present study, 6061 and A356 based nano-composites are fabricated by using the ultrasonic stirring technology (UST) in a coreless induction furnace. SiC nanoparticles are used as the reinforcement. Nanoparticles are added into the molten metal and then dispersed by ultrasonic cavitation and acoustic streaming assisted by electromagnetic stirring. The applied UST parameters in the current experiments are used to validate a recently developed magneto-hydro-dynamics (MHD) model, which is capable to model the cavitation and nanoparticle dispersion during UST processing. The MHD model accounts for turbulent fluid flow, heat transfer and solidification, and electromagnetic field, as well as the complex interaction between the nanoparticles and both the molten and solidified alloys by using ANSYS Maxwell and ANSYS Fluent. Molecular dynamics (MD) simulations are conducted to analyze the complex interactions between the nanoparticle and the liquid/solid interface. The current modeling results demonstrate that a strong flow can disperse the nanoparticles relatively well during molten metal and solidification processes. Molecular dynamics simulation results prove that ultrafine particles (<< 1 µm) will be engulfed by the solidification front instead of being pushed, which is beneficial for nano-dispersion. Experimental results confirm that the nanoparticles are dispersed reasonably well in the metal matrix, but some insignificant agglomeration still occurs. Besides, SEM/EDS results show that C element tends to gather around the grain boundary area where the Si eutectic phase is located. (Published By University of Alabama Libraries

CFD Modeling and Simulation in Materials Processing 2018

This book contains the proceedings of the symposium “CFD Modeling and Simulation in Materials Processing” held at the TMS 2018 Annual Meeting & Exhibition in Phoenix, Arizona, USA, March 11–15, 2018. This symposium dealt with computational fluid dynamics (CFD) modeling and simulation of engineering processes. The papers published in this book were requested from researchers and engineers involved in the modeling of multiscale and multiphase phenomena in material processing systems. The symposium focused on the CFD modeling and simulation of the following processes: Additive Manufacturing (Selective Laser Melting and Laser Powder Bed Fusion); Gas Atomization, Iron and Steelmaking (Continuous Casting, Blown Converter, Reheating Furnace, and Ladle Metallurgical Furnace); Submerged Arc Furnaces; Electrokinetic Deposition; Core Injection Molding; Evaporation of Metals; Friction Stir Welding; Ingot Casting; High Pressure Die Casting; and Casting and Solidification with Electromagnetic Field Interaction. The symposium also covered applications of CFD to engineering processes and demonstrated how CFD can help scientists and engineers to better understand the fundamentals of engineering processes