Defects and Properties of Cast Metals: Defects II & Properties I
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; Charles Monroe, University of Alabama Tuscaloosa
Monday 2:30 PM
February 24, 2020
Room: 17B
Location: San Diego Convention Ctr
Session Chair: Alex Plotkowski, Oak Ridge National Laboratory; Matthew Krug, Air Force Research Laboratory
2:30 PM Invited
Coupling Hot-tearing of High γ’ Nickel Alloys to Processing Parameters Through Classic Solidification Criteria: Kevin Chaput1; Matthew Krug1; Edwin Schwalbach1; 1Air Force Research Labroatory
One of the primary limitations in wider adoption of laser powder bed fusion (LPBF) technology is formation of hot-tears characteristically observed in high strength aluminum and high γ’ nickel alloys, key engineering alloys for aerospace applications. Fortunately, with an understanding of the appropriate boundary conditions of the process, there exists decades of welding and solidification theory that can be leveraged to address these defects. This body of work focuses on understanding the hot-tearing mechanism observed in CM 247LC fabricated by LPBF and the applicability of hot-tearing criteria derived for castings and welds. Leveraging a fast-acting thermal model, this work couples process conditions (power, velocity, hatch spacing, etc.) to key solidification parameters (thermal gradient, isotherm velocity) with coupled experimental results for validation. This methodology will be used to develop and demonstrate a strategy to control the formation of these defects while delivering a dense component.
3:00 PM
Controlling Freckle Defect Formation Using Magnetic Fields: Andrew Kao1; Ivars Krastins1; Natalia Shevchenko2; Sven Eckert2; Koulis Pericleous1; 1University of Greenwich; 2HZDR
Freckles are a common microstructural defect that leads to discontinuity in material properties of cast alloys, that form when solute channels solidify. X-ray radiography experiments using a GaIn alloy have captured the freckle formation process in situ. Applying a static magnetic field to the process, introduces two phenomena. The first is Electromagnetic damping that slows flow across flux lines, the second is a thermoelectric magnetohydrodynamic force that encourages flow between dendrites. Using TESA, the Thermoelectric Solidification Algorithm, running in parallel on a high performance computing cluster, a validated microscopic numerical model has been developed that captures the inter-dendritic flow that feeds the emerging freckle at the scale of the experimental sample. The simulations increase our understanding of this process and show that judicious application of the magnetic field can disrupt the formation of freckles and has the potential to eliminate them.
3:20 PM
The Prediction of Solidification Defects: A Multi-defects Modeling: Jun Li1; Hongbiao Dong1; 1University of Leicester
Based on the established dendritic-equiaxed & columnar macrosegregation model, a four-phase solidification model that further consider the gas phase, which supplements the volume reduction of solidification shrinkage, has been established to realize the prediction of shrinkage. For the prediction of inclusion, in order to distinguish the difference between exogenous and endogenous inclusions, two models had been established respectively: 1) for exogenous inclusions, the coupling of Discrete Phase Model (DPM) and four-phase solidification has been considered, which has the possibility to track the moving of inclusion particle; 2) for endogenous inclusions, inclusion-combined macrosegregation model, which coupling the inclusion growth theory with the multicomponent four-phase solidification model, has been established. This multi-defects model has been implemented on the solidification process of steel ingot to investigate the formation process of macrosegregation, shrinkage cavity, porosity, and inclusion defects. The strong interaction behaviors between the shrinkage cavity, inclusion and macrosegregation had been observed.