Defects and Properties of Cast Metals IV: 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; Andrew Kao, University of Greenwich; Kyle Fezi, Fort Wayne Metals
Monday 2:00 PM
February 28, 2022
Room: 210B
Location: Anaheim Convention Center
Session Chair: Kyle Fezi, Fort Wayne Metals ; Paul King, Ampere Scientific
2:00 PM Invited
Elucidating the Relationship between Arc Behavior and Solidification Defects during Vacuum Arc Remelting of Superalloys: Daniel McCulley1; Joshua Motley1; Matthew Cibula1; Paul King1; 1Ampere Scientific
Measurements of external magnetic fields during vacuum arc remelting (VAR) provide information on the distribution and location of arc distributions during processing. Arc dynamics have been proven to be connected to solidification defects through disturbances in the heat flux and the generation of conditions that lend themselves to inclusion entrainment. An enticing pathway to ensure and/or improve the quality of certain superalloys is through monitoring and control of the arc dynamics. Ampere Scientific has shown the ability to distinguish between normal and off-normal arc conditions during operations through careful analyses of magnetic fields generated by the arcs across the arc gap. For example, constricted arcs during superalloy processing have no overt signature in traditional VAR process signals, however the magnetic field variances provide instantaneous feedback as to their occurrence. Here we present our work towards characterizing the relationship between arc behavior and solidification defects using the VARmetric measurement system.
2:25 PM
Controlling Freckle Defect Formation Using Magnetic Fields: Andrew Kao1; Natalia Shevchenko2; Xianqiang Fan3; Catherine Tonry1; Peter Lee3; Sven Eckert2; Koulis Pericleous1; 1University Of Greenwich; 2Helmholtz-Zentrum Dresden-Rossendorf; 3UCL
The application of a static magnetic field has been shown to have a significant effect on channel formation in the GaIn freckle defect forming alloy. The underlying mechanisms are via Thermoelectric Magnetoydrodynamics (TEMHD) driving inter-dendritic fluid flow. Thermoelectric currents form due to the inherent thermal gradient and spatial variation in composition due to solute partitioning. In the presence of a magnetic field these currents interact generating the flow driving Lorentz force. Convective solute transport then alters solidification behaviour. This causes spatial repositioning of the channel, preferential growth, secondary effects such as plume migration and complex grain boundary interactions. TESA (ThermoElectric Solidification Algorithm) is a parallel Cellular Automata Lattice Boltzmann based numerical model that has been validated against Xray synchrotron experiments. Using TESA the dependency of the magnetic field orientation and magnitude has been explored, providing further predictions for controlling the channel.
2:45 PM
Improving Material Properties Using Contactless Ultrasonic Cavitation: Catherine Tonry1; Agnieszka Dybalska2; Valdis Bojarevics1; Georgi Djambazov1; William Griffiths2; Koulis Pericleous1; 1University of Greenwich; 2University of Birmingham
Ultrasonic Treatment (UST) of liquid metals has shown great potential for both grain refinement and the degassing of molten metals. Current UST methods use an immersed sonotrode to treat the melt. One of the main problems with this approach, is that contact with the melt can introduce impurities and the sonotrode can also be dissolved. By using a high frequency electromagnetic coil to induce ultrasound in the melt contact can be avoided, while adding heat and mixing. To ensure the resulting pressure waves reach the level required for cavitation it is necessary to tune the system for acoustic resonance. Extensive studies in aluminium, have shown that this technique can produce grain refinement and enhance degassing. Recent work has now demonstrated that castings produced using this method have increased %Elongation and tensile strength. Since there is no contact involved, this contactless sonotrode can be used for high temperature or reactive melts.
3:05 PM
Formation Mechanisms of Surface Blistering in AA6xxx Rolled Products: Microstructure Characterization, Ultrasonic Analysis, and Rolling Tests: Pascal Gauthier1; Mousa Javidani2; Tao Wang1; John Evans3; 1Rio Tinto; 2Université du Québec à Chicoutimi; 3Constellium
The evolution mechanisms of a non-hydrogen related blister defect on the 6xxx rolled aluminum sheets were investigated in this paper. It is revealed that aluminum sheet could still be susceptible to blistering even when the as-cast ingot has minimum residual hydrogen contents and presents no sign of any foreign materials or large inclusion populations. In those cases, all the blisters were aligned in the rolling direction and small aluminum oxide particles and films were found near to the defective areas. These observations suggest the blister defects originated from the as-cast ingot material surfaces. Hot and cold rolling simulation tests conducted using laboratory scale rolling machines demonstrated the defect evolvement from the ingot short face imperfection into blisters on the sheet products. In this study, a variety of rolling conditions were also tested for their effects on subsurface delamination prevention.
3:25 PM Break
3:45 PM
3D Characterization of Competitive Dendrite Growth and On the Role of Low Angle Grain Boundaries during Solidification of Single Crystal Ni-based Superalloys: Felicitas Scholz1; Pascal Thome1; Jan Frenzel1; Gunther Eggeler1; 1Ruhr-University Bochum
The present work investigates competitive dendrite growth during Bridgman solidification of single crystal Ni-based superalloys of CMSX-4 type. A novel tomographic metallographic approach based on serial sectioning, optical wide-field micrographs and quantitative image analysis was applied to evaluate the growth of over 2500 dendrites in a large specimen volume. Our technique involves Voronoi tessellation analysis of micrographs to study competitive dendrite growth. Special emphasis is placed on crystal mosaicity and the presence of low angle grain boundaries. Distributions of neighbour dendrite coordination numbers and of primary dendrite arm spacings were evaluated. It was found that there is increased extinction and re-emergence activity of dendrites in regions with a higher degree of mosaicity. We discuss our results in the light of the present state of knowledge on competitive dendrite growth and related research on low-angle boundary defects in single crystal superalloys.
4:05 PM Cancelled
Evolution of Microstructure and Mechanical Properties of the As-cast 1030B Al Sheet during Ultrasound-assisted Continuous Casting: Ripeng Jiang1; Wenhao Zhao1; Li Zhang2; Xiaoqian Li1; Shaokang Guan2; 1Central South university; 2Zhengzhou University
Continue Casting Direct Rolling (CCDR) is an efficient process for aluminum plates and strips production. However, unlike steel sheet, there is no homogenizing process for the as-cast Al billet before direct rolling. Thus, the quality of the as-cast billet has a great influence on the performance of the final hot-rolled strip. In order to reduce the defects in the microstructure of the as-cast billet, four-source ultrasonic treatment was firstly applied in the continuous casting during the CCDR process of 1030B Al sheet. The evolution of microstructure and mechanical properties of the as-cast 1030B Al sheet under ultrasonication were investigated. Results indicated that the α-Al grains were refined by 30% under ultrasound, which may be attributed to the increased Ti content in the Al matrix by the ultrasonic dispersion. Meanwhile, the mechanical properties of the sheet were also increased after ultrasonic treatment.