Materials Research in Reduced Gravity: Solidification
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Solidification Committee, TMS: Process Technology and Modeling Committee
Program Organizers: Wilhelmus Sillekens, European Space Agency; Michael Sansoucie, Nasa Marshall Space Flight Center; Robert Hyers, Worcester Polytechnic Institute; Douglas Matson, Tufts University; Gwendolyn Bracker, DLR Institute of Materials Physics in Space
Wednesday 2:00 PM
March 22, 2023
Room: 30B
Location: SDCC
Session Chair: Robert Hyers, Worcester Polytechnic Institute; Maike Becker, German Aerospace Center (Dlr)
2:00 PM
Solidification of Al-Cu Alloys in Microgravity and Terrestrial Environments: Thomas Williams1; Christoph Beckermann1; 1University of Iowa
Buoyancy of the equiaxed grains can significantly affect the microstructure of cast metals including the Columnar to Equiaxed Transition (CET). Benchmark solidification data that accounts for buoyancy of the solid is limited. A series of solidification experiments were conducted identically on earth and aboard the International Space Station. Al-4, 10, and 18wt.%Cu samples were solidified which have primary solids with negative, neutral, and positive buoyancy relative to their molten liquid. Solidified samples revealed drastically different microstructural features between microgravity and terrestrial cases. All microgravity experiments and the Al-18wt.%Cu terrestrial experiment produced an entirely equiaxed grain structure. The Al-4 and 10wt.%Cu terrestrial experiments produced a CET. The Al-4 and 18wt%.Cu terrestrial experiments showed evidence of grain sedimentation and floatation respectively. Eutectic area fraction, macrosegregation, and thermal process parameters are characterized for all experiments.
2:20 PM
In-situ Investigation of the Impact of Gravity on CET during Directional Solidification of Al-Cu Alloys: Guillaume Reinhart1; Fabiola Ngomesse1; Lara Abou-Khalil1; Gerhard Zimmermann2; David Browne3; Wilhelmus Sillekens4; Henri Nguyen-Thi1; 1Aix-Marseille University; 2ACCESS e.V.; 3University College Dublin; 4European Space Agency
During industrial processes such as casting, welding or additive manufacturing, a transition between a columnar grain structure and an equiaxed grain structure is often observed. The so-called Columnar-to-Equiaxed Transition (CET) has a major impact on the mechanical properties and lifetime of metal parts. Gravity is the cause of many phenomena such as natural convection and buoyancy that impede the understanding of the solidification process, and specifically the CET. X-radiography has become a powerful technique to investigate the microstructure formation dynamics in metal alloys, and especially gravity-induced effects that are transient phenomena. The present communication will provide an overview of results obtained by in-situ observation of directional solidification experiments carried out on Al–Cu alloys. Two microgravity platforms were used: parabolic flights and sounding rockets. The comparative analysis with ground-based experiments will enlighten the impact of gravity-related effects during the various steps involved in the CET.
2:40 PM
Nucleation and Growth Dynamics of Equiaxed Dendrites in Thin Metallic Samples in Microgravity and on Ground: Maike Becker1; Mareike Wegener1; Jörg Drescher1; Florian Kargl1; 1German Aerospace Center (DLR)
In situ X-radiography observations of the solidification of binary metallic alloys give valuable insights into the development of the microstructure. In this study, the nucleation and growth characteristics of equiaxed dendrites in near-isothermal solidification experiments, performed during two sounding rocket missions, MAPHEUS-6 and 7, are presented. Samples of the composition Al-15 wt.%Cu and Al-46 wt.%Ge were processed in microgravity and several samples on ground. The measured dendritic growth rates and observed concentration distributions in the liquid indicate no difference between microgravity and on-ground horizontal solidification experiments in line with previous observations. On the contrary, a difference in the nucleation behavior was found. In all microgravity experiments bursts of nucleation were observed, which is different from comparable on-ground experiments, where nucleation occurs continuously. The findings suggest that small convective flows still present in thin samples affect nucleation undercooling resulting in different nucleation behavior on Earth and in microgravity.
3:00 PM
Analysis of In-Situ Microgravity Equiaxed Solidification Experiment using Machine Learning and Advanced Ground-Based Characterization Techniques: Jonathan Mullen1; Shashidhara Marathe2; Saranarayanan Ramachandran3; Wajira Mirihanage3; David Browne1; 1University College Dublin; 2Diamond Light Source; 3University of Manchester
A combined Machine Learning and modular image analysis approach has been used to automatically process and interrogate quantitatively an in situ X-ray video-microscopy sequence of equiaxed solidification of an Al-20wt.% Cu alloy, executed under microgravity conditions on board the Maser-13 sounding rocket. The 3D dendritic structure of the as-flown microgravity sample was then revealed by synchrotron X-ray computed microtomography. Crystallographic orientations of the dendrites were also extracted using electron backscattered diffraction, yielding extended microstructural details at micron resolution. In this way the nucleation, growth, orientation and final inclinations of all the equiaxed dendrites have been quantified and correlated, providing high quality benchmark data on the evolution of the equiaxed microstructure under diffusion-controlled conditions.
3:20 PM
CAPTN Simulation of Dendritic Grain Structures: Yijian Wu1; Oriane Senninger1; Charles-Andre Gandin1; 1PSL University
The Cellular Automaton - Parabolic Thick Needle (CAPTN) method is developed to compute dendritic microstructures. A dendritic branch is modeled as a cylinder headed by a parabolic tip. Its kinetics is computed using the composition field in the liquid in the vicinity of the parabola. Implementation involves the finite element method together with adapted mesh. The dendritic branch takes part in the definition of a grain envelope by its integration in a cellular automaton growth algorithm. Application is demonstrated to competition taking place among columnar dendritic grains forming as a result of directional solidification and to the growth equiaxed dendritic grains, both in two and three dimensions. Results are compared with existing numerical solutions, showing promising results for application to experiments conducted in reduced gravity.
3:40 PM Break
4:00 PM
Structure and Properties of the Solder Joints Produced in Terrestrial and Microgravity Environment: Manish Kumar1; Sid Pathak1; 1Iowa State University
Using Lead-Tin (40wt%Pb-60wt%Sn) solders from the In-Space Soldering Investigation, along with freshly made terrestrial solders of the same composition, we demonstrate how the lack of Earth’s natural convective flow and buoyancy effects during melting/solidification onboard the International Space Station affects its microstructure and properties. Our scanning electron microscopy and Micro-computed tomography analysis demonstrate a considerable amount of internal porosity (about four times that of terrestrial solder) in the microgravity solder. We also performed a detailed analysis of the substantial effect of aging on the ISSI solder microstructure and properties over the past 17 years. Additionally, we report on the micro-mechanical behavior of the solder joints under extreme conditions of cryogenic temperatures similar to those typically experienced by the ISS (-150oC on shady side outside the ISS). These tests examine the effects of β-to-α phase transformation in Sn below 13oC and the associated volume and internal stress changes in Pb-Sn solders.
4:20 PM
Gravity Influence on the Distortion-Densification Trajectory for Liquid Phase Sintering: Randall German1; Elisa Torresani1; Eugene Olevsky1; 1San Diego State University
Sintering techniques are employed in the production of precise and complex engineering components. Usually the formation of a liquid phase accelerates sintering. However, a liquid phase can contribute to nonuniform dimensional changes that result in component distortion. Several factors can induce nonuniform shrinkage, including gravity. This analysis examines how the pore structure influences distortion during sintering. When sintering on Earth, low dihedral angle systems lose rigidity when the pores saturate, leading to a loss of component strength and distortion. In microgravity sintering, pores coalesce resulting in reduced capillarity, and densification halts at less than full density. Microgravity sintering can result in distortion with incomplete densification. Several factors are isolated to show the conditions where distortion with incomplete is expected based on microgravity experiments.