Defects and Properties of Cast Metals IV: Defects III- Porosity & Cracking
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Solidification Committee
Program Organizers: Lang Yuan, University of South Carolina; Brian Thomas, Colorado School of Mines; Peter Lee, University College London; Mark Jolly, Cranfield University; Alex Plotkowski, Oak Ridge National Laboratory; Andrew Kao, University of Greenwich; Kyle Fezi, Fort Wayne Metals
Tuesday 4:00 PM
March 1, 2022
Room: 210B
Location: Anaheim Convention Center
Session Chair: Alex Plotkowski, Oak Ridge National Laboratory
4:00 PM Invited
Quantifying Pore Evolution during Laser Powder Fusion Using High-speed X-ray Imaging and High Fidelity Multiphase Simulation: Chu Lun Alex Leung1; Michael Mallon2; Dawid Luczyniec2; Yuze Huang1; Samuel J. Clark3; Yunhui Chen1; Sebastian Marussi1; Lorna Sinclair1; Margie P. Olbinado4; Elodie Boller5; Alexander Rack5; Iain Todd6; Peter D. Lee1; 1University College London; 2European Space Agency; 3Argonne National Laboratory; 4Paul Scherrer Institute; 5European Synchrotron Radiation Facility; 6University of Sheffield
Laser powder bed fusion additive manufacturing (LPBF) produces complex net-shape parts from alloy powders, in a layer-by-layer manner. X-ray imaging studies of pore evolution mostly focus on single-layer tracks on substrates, missing the interaction of the laser beam with pre-existing pores in prior layers. Here, we used an in situ and operando process replicator (ISOPR), synchrotron X-ray imaging and high fidelity simulation to monitor and elucidate the process dynamics during a multilayer build of a Ni-superalloy. We quantify the changes in keyhole geometry, porosity, and remelting zone, as a function of time, layer number, and local layer thickness. These results were compared with a multiphase and multiphysics simulation to reveal the solid-liquid-gas-metal vapour interaction, keyhole evolution mechanisms, melt pool, and porosity. This work highlights the impact of layer thickness on build quality for powder bed fusion processes and suggests ways to mitigate the formation of imperfections.
4:25 PM
Porosity Formation in High Pressure Die Casting: Experiments and Simulations: Nicole Trometer1; Xuejun Huang1; Michael Moodispaw1; Jianyue Zhang1; Alan Luo1; 1Ohio State University
Porosity formation in high pressure die casting (HPDC) of aluminum and magnesium alloys is very complex, and is related to many factors such as entrapped air, dissolved gases and alloy shrinkage during solidification. This talk will present our recent experimental and computational investigations of porosity formation during HPDC. Water analog experiments were conducted to validate the effect of vacuum on flow and air entrainment, and compared to process simulation by ProCAST. A three-dimensional cellular automaton was developed to predict solidification microstructure and microporosity evolution during casting. HPDC experiments were carried out on two aluminum alloys at three vacuum levels. The porosity in HPDC samples was characterized using metallography, density measurements, computed tomography (CT) and micro-CT scanning. The decrease in porosity in vacuum die casting was in agreement with simulations. Finally, the porosity was related to the mechanical properties of die cast alloys in various vacuum levels.
4:45 PM
Nucleation in Undercooled Melt upon Changes in the Electromagnetic Stirring: Gwendolyn Bracker1; Stephan Schneider2; Juergen Brillo2; Georg Lohoefer2; Robert Hyers1; 1University of Massachusetts; 2Deutsches Zentrum für Luft- und Raumfahrt (DLR)
Electromagnetic levitation (EML) experiments provide access to undercoolings, similar to the undercooling that has been observed on the boundaries of continuous casting. Undercooling near the meniscus can increase the incidence of meniscus hooks which in turn entrap inclusions and increase defects present in castings. Current work is exploring nucleation events in undercooled melts that may have been caused by electromagnetic stirring- which is often used in continuous casting. During experiments in the ISS-EML facility, molten samples, held at a constant temperature, were levitated for several minutes before the sample solidified. Experiments were conducted in 2020 to investigate additional solidification phenomena in which a step change to the electromagnetic field was applied to the sample, intended to induce surface oscillations; instead, the sample solidified. The recent experiments confirmed this nucleation event several times using a zirconium-nickel sample. It is hypothesized that the nucleation is caused by electromagnetically-driven flow in the sample.
5:05 PM Concluding Comments