The DEvice for the study of Critical LIquids and Crystallization - Directional Solidification Insert-Reflight (DECLIC DSI-R) investigation, a follow-on to the DSI study, is designed to quantitatively examine three-dimensional pattern evolution, dynamics and the relationship between micro- and macrostructure formation during solidification processes. The main goal of the DSI-R investigation is to examine and measure the fundamental physics controlling the temporal and structural organization and evolution of secondary dendritic, branch-like structures and their interaction with the array of primary branches under directional solidification conditions. By observing these phenomena in a microgravity environment, it is possible to refine the theoretical models and numerical simulation predictions, which ultimately results in an improvement of industrial ground-based material development processes.Principal Investigator(s)
Centre National d?Etudes Spatiales, Toulouse, , France
National Aeronautics and Space Administration (NASA)Sponsoring Organization
Human Exploration and Operations Mission Directorate (HEOMD)ISS Expedition Duration:
September 2012 - October 2013
33/34,35/36Previous ISS Missions
The Directional Solidification Insert Reflight (DSI-R) investigation involves the study of directional solidification in relation to SCN-based bulk alloys (succinonitrile-a transparent organic substance in the liquid state that is used to study the phenomena related to solidification processes) and transparent model alloys. This includes investigating the birth and growth of morphological instabilities at the solid-liquid interface and the effects of coupling between the solidifying interface and areas of convection, through a systematic variation of process parameters such as temperature. By observing these phenomena in a microgravity environment, it is possible to refine the theoretical models and numerical simulation predictions, which ultimately results in an improvement of industrial ground-based material development processes. The goal of these reduced-gravity experiments on ISS is to obtain benchmark data on cellular and dendritic microstructure formation under diffusive transport conditions. This investigation directly addresses outstanding issues that remain open in the understanding of complex dendritic microstructures.
From an engineering point of view, the DECLIC hardware uses two International Space Station (ISS) program-provided lockers comprised of the lower locker called the ELectronic Locker (ELL), which houses power supplies, data handling and central regulation electronics for operation and control. This lower locker contains all necessary electrical and electronic systems that permit the facility to operate in an autonomous mode or with telescience interactions from the scientific team at the dedicated user center. The upper locker is the EXperiment Locker (EXL). It contains the DECLIC optical bench that receives the investigations cartridge insert which contains a specific scientific material being examined. This optical bench contains all optical and opto-electronic sensors that are necessary to perform measurements at low or high rate of acquisition.
The DECLIC DSI-R investigation is operated by the Central Regulation Electronics (CRE), located in the EXL of the DECLIC instrument. The CRE controls several functions such as: running thermal control algorithms; making a precision acquisition of temperature sensors used by the thermal control algorithm; supplying accurate electrical voltages to be width modulated by insert electronics for heating elements; controlling power to heating elements; controlling cartridge insert speed inside the furnace; and managing the safe status of the cartridge insert (i.e., to prevent overheating).
Precise measurement of interface shape and geometrical characterization of cellular and dendritic patterns, as well as of individual cell or dendrite is carried out as a function of time for different values of composition, growth rate and temperature gradient. These measurements are used in combination with modeling and numerical simulations of the temperature fields in order to establish the physics that govern the dynamics of interface pattern selection, and finally to quantitatively determine the conditions for the planar to cellular and cellular to dendritic transitions. Optical observations of the solidification front is done either directly or by interferometry (imaging using the interference fringes resulting from the recombination of reference and object light beams issued from the same coherent source) with the cartridge placed in one arm of a Mach-Zehnder interferometer (a device used to determine phase shifts caused by the solidifying sample which is placed in the optical path of the object beam).
The DECLIC facility provides power, communications, command/control, data storage, and multiple, flexible optical capabilities in support of each investigation. DECLIC-DSI-R involves investigating the birth and growth of morphological instabilities and the effects of coupling between the solidifying interface and the convection. By observing these phenomena in a microgravity environment, it becomes possible to refine the theoretical models and numerical simulation predictions. The capability to quantitatively predict resultant material properties for alloys solidified in reduced gravity environments may be critical to developing in-situ processing techniques necessary to attain future exploration objectives.Earth Applications
DECLIC-DSI-R provides additional insight into the fundamental physics that govern the formation and selection of solidification patterns. This investigation also provides an opportunity to gain an insight into the general problem of pattern formation, as solidification patterns are recognized to be similar to those forming in many other branches of science. In particular, the sidebranch instability under investigation is crucial for dendritic growth and for determining the solute segregation pattern in the “mushy” zone that largely governs the properties of cast alloys. Increased understanding of these fundamental processes will ultimately result in the development of more rigorous and dynamic models of microstructure formation that are critical for the design of processing conditions required for the development of advanced materials of commercial importance.
After the DSI-R is installed by the crew, the DECLIC runs automatically following a timeline of sequences that are commanded by the payload control center (CADMOS in Toulouse, France). The data transmitted to ground by real time telemetry allows the investigation team to monitor the health and status. Yet, due to telemetry bandwidth limitations, the entire data set cannot be downlinked and is therefore copied to a Removable Hard Disk Drive (RHDDs) for future return to the ground. The data is then transferred and stored at the CADMOS operational center, and available for the research teams to process and review.Operational Protocols
The ISS crew installs the DSI-R hardware into the DECLIC payload facility and then powers facility on. Crew participation is not required during investigation runs excepted for the changing out of full Removable Hard Disk Drives (RHDDs). Typically, once the DSI-R is inside DECLIC, the investigation consists of running several successive melting-solidification cycles over a specified period of time.