Coarsening in Solid Liquid Mixtures-4 (CSLM-4) - 08.18.16
The Coarsening in Solid Liquid Mixtures-4 (CSLM-4) investigation studies growth and solidification processes in tin-lead mixtures that contain a small amount of tin dendrites. Some metal alloys form tiny branching structures called dendrites when they crystallize, and the size, spacing, and interlocking of these dendrites play an important role in determining their physical properties such as softness, hardness, or brittleness. The microgravity environment of the International Space Station enables scientists to study dendritic growth without any interference from gravity to improve our knowledge of materials science, potentially leading to making new alloys with enhanced properties. Science Results for Everyone
Information Pending Experiment Details
Peter W. Voorhees, Ph.D., Northwestern University, Evanston, IL, United States
NASA Glenn Research Center, Cleveland, OH, United States
ZIN Technologies Incorporated, Cleveland, OH, United States
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
Human Exploration and Operations Mission Directorate (HEOMD)
Earth Benefits, Scientific Discovery
ISS Expedition Duration
March 2014 - September 2015
The initial CSLM-2 investigations were conducted during ISS Increment 7. CSLM-2 high volume fraction samples were conducted during ISS Increment 16/17. CSLM-2R with low volume fraction samples were conducted during Increment 23/24. CSLM-3 dendritic growth samples were conducted during ISS Increment 33/34, and 35/36.
- CSLM-4 is a material science investigation that studies the coarsening of dendrites in solid-liquid mixtures at low volume fractions of solid. This low volume fraction enables the examination of the coarsening of a single or a few dendrites at a time; something that is impossible on the ground.
- The shape of the dendrite is determined by measuring the morphology of the dendrite as a function of position from the tip. This allows researchers to investigate beyond classical secondary arm spacing measurements.
- CSLM-4 also studies the three-dimensional topology of the solid liquid mixtures. In particular this study shall focus on topological singularities that occur when a secondary dendrite separates from the main dendrite stem or when two arms fuse together.
- The CSLM-4 investigation requires reduced gravity found on the International Space Station (ISS) that allows for unprecedented insights into the coarsening of dendrites due to the elimination of sedimentation. Ground-based experiments show that the effects of sedimentation cause secondary dendrite arms to float away from primary dendrite arms; this limits measurement of the rate in which topological singularities occur and the rate at which the structure breaks up.
- In a microgravity environment it is possible to examine the evolution of the morphology of the mixtures in the diffusive limit where the concentration field is set by the curvatures of the solid-liquid interfaces.
- The CSLM-4 investigation will process 6 Sample Processing Units in the MSG on board the International Space Station during Increment 41/42.
In the predecessor CSLM-3 study, samples are a mixture consisting of Sn (tin)-rich particles in lead-tin liquid, a mixture that has a low sintering temperature and a high coarsening rate; making it perfect for studying the process of Oswald ripening. Sample runs are conducted inside the sealed MSG work volume using existing CSLM hardware.
The CSLM-4 investigation further examines metal dendrites (i.e., tree-like structures) that form during the quenching and solidification of molten metals. The spacing between the branches of the dendrite controls the mechanical properties of the solidified metals, such as engine blocks used in car engines. During the casting process the dendrites undergo a process called coarsening. During coarsening the dendrites change their shape, with a change in the spacing between the branches of the dendrites. Since the spacing alters the mechanical properties of the alloy, the coarsening of dendrites has a major effect on the properties of metal alloys. The objective of this experiment is to investigate this coarsening process without the complicating effects of convection of the liquid or sedimentation (e.g., gravity induce effects) of the dendrites.
Samples are processed inside a Sample Processing Unit (SPU), which has a cylindrical sample chamber. Each SPU contains 4 samples and crew members must load each SPU and initiate runs individually. Samples are heated to 185 degrees Celsius to enable dendrite growth. This temperature is maintained for various, predetermined intervals. Each heating time is unique for each SPU. After an SPU is processed, pressurized water is released into the chamber to quench the sample, cooling it down to lock in the structures. During a normal sequence the quench cycle is initiated automatically by the Electronic Control Unit (ECU). Quenching can be initiated manually if needed.
Data captured by the ECU is transferred to the MSG laptop for storage and down loading to the ground-based researchers. The ECU provides power and controls all stages of the sample processing and experimental parameters and status are displayed on the ECU’s LCD display screen. The ECU also controls the temperature inside the SPU sample chamber and monitors and records the sample’s temperature. A baseplate is used to attach the SPU and ECU to the Microgravity Science Glovebox (MSG) work volume floor.
Alloys' properties are strongly linked to their dendritic makeup and the spaces between the individual branches. Understanding the controlling factors in the growth of dendrites is crucial for developing accurate computer simulations and manufacturing techniques. On Earth, gravity affects the growth and solidification process (called coarsening), so microgravity-based experiments are necessary to better understand the true nature of dendrite growth. New insights into dendrite formation and alloy behavior are used to design lighter and stronger materials for use in space exploration.
Understanding how temperature and time affect the growth of dendrites helps researchers to develop more efficient and economical means of producing higher quality products from the casting of molten metals. CSLM series of experiments provide insights into new physics that can be used by alloy scientists and engineers to enhance the properties of important materials used in the manufacturing jet turbine blades, automobile engine components, and support structures for buildings and bridges.
Operational Requirements and Protocols
The crew unstows and sets up the CSLM-4 hardware (ECU, first SPU, baseplate, cables, and vacuum hose) in the MSG and runs any necessary vacuum cycles before testing each SPU which contains the lead-tin samples. Sample heating runs are initiated using a toggle switched on the ECU. Once started, the investigation runs autonomously. Individual SPU heat soak times range from 10 min, 15 min, 30 min, 1 hour, 5 hours, and 15 hours, followed by a quench cycle. When an individual sample run is completed, the crew downloads data from the ECU to the MSG laptop and switches samples by removing the SPU and replacing it with a new SPU. Once all runs have been completed, the hardware is removed from the MSG work volume and stowed. The processed SPU’s are stored on ISS until they can be returned to Earth. On Earth, the researchers analyze each sample for particle size distribution, particle morphology, matrix structure, and particle crystallographic orientation.
Decadal Survey Recommendations
Applied Physical Science in Space AP9
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Glenn Research Center - SFS
Flight hardware installed in the Microgravity Science Glovebox on ISS showing: (a) the sample processing unit (SPU), the electronics control unit (ECU), and the space acceleration measurement system (SAMS); (b) hardware overview of the sample chamber in the SPU. (NASA Image)
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One of the six Sample Processing Units (SPUs) used on the International Space Station. The SPUs contain the Coarsening in Solid-Liquid Mixtures dendrite samples. (Credit: NASA)
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Coarsening in Solid-Liquid Mixtures-3 dendrite sample ground test showing sedimentation. (Image Credit Peter Voorhees, Northwestern University)
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Time-dependent evolution of the structures in three dimensions in situ through X-ray microtomography. (Image Credit Peter Voorhees, Northwestern University)
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