The objective of this collaborative research is a scientific understanding sufficient to enable casting of metallic sheets, ribbon or foil, of commercially acceptable quality, directly from the molten metal state. Experimental testing along side computational and mathematical modeling will be used to achieve the desired understanding. From aluminum foil to airplane wings, most metallic components used today are formed from flat pieces. As in current commercial practice, mechanical rolling and thermal annealing stages have high energy, environmental and capital costs. The goal is to develop processes to solidify raw material directly into final product, without downstream processing steps. This is a vision that goes back to Bessemer (1865) and its realization would revolutionize thin-sheet manufacturing. The casting method forces molten metal into contact with a spinning cold wheel where the metal solidifies and is spun off. Manipulation of the contacting and solidification events is the focus.
As compared to current practice, there would be direct energy savings for single-step casting. Indirect benefits include the reduction of greenhouse gases, particularly, carbon dioxide. Capital costs for manufacturing would be reduced and productivity would be increased. Both environment and industry benefit. As China and India industrialize and the demand for flat products grows, these benefits to society will accrue. A further benefit will be through education. Undergraduates and graduates will be involved in this research as a problem-solving team, with educational outreach to local schools.
The goal of this project is to develop high speed continuous casting processes that solidify molten metal directly into final product. At processing speeds of meters-per-second, this kind of fabrication means high productivity. High processing speed also means rapid solidification which can yield special material properties for certain alloys. Examples are the metallic glass cores that enable ultra-efficient power distribution transformers. In summary, energy saving processes and energy saving applications benefit from our project discoveries. The context of the project is continuous casting using planar flow melt-spinning (PFMS). In PFMS, liquid metal is forced into contact against a cooler wheel substrate where it is solidified and spun off as a thin ribbon product, all in a single step. Defect formation, sticking distance and product thickness control are specific problems that arise in PFMS. We have discovered the scientific basis for these problems, and have thereby suggested engineering solutions. Intellectual Merit. The science behind defect formation and sticking distance has been discovered, with validation using the PFMS process to cast aluminum and aluminium alloys. This scientific foundation extends to other cast materials and likely to other high speed casting processes. Our engineering approach is to manipulate the contacting and forming event at length-scales that were previously not accessible. Our science outcomes indicate how product can be manipulated and builds upon the technology basis provided by our previous patents for the 'Gutenberg meets Bessemer' approach to casting-by-design, US patents 7,306,025 and 7,082,986. Broader Impact -- human resources. Two PhD students (US citizens, both) have been trained to help meet our national demand over the next half-century for technical leadership in science and engineering. Nine undergraduates have been exposed to the excitement of a scientifc research project with practical engineering consequences, a project that involves experiment, analytical and computational modeling. More often than not, undergraduates involved in our projects have gone on to PhD programs. Broader Impact -- techonology. To the extent that contacting and phase-change are at the heart of many fabrication processes, the scientific base we have developed for the contacting, forming and solidification in high-speed solidification processing of metals will benefit other fabrication processes using other materials. Broader Impact -- society. Impacts of this project on society relate to saving energy and the consequent mitigation of climate change. At present, commercial use of single-step thin metal processing is the exception rather than the rule. To the extent that our project lays a scientific foundation sufficient to enable more exceptions and fewer rules, society will benefit, as illustrated below using aluminum foil as an example. At present, planar flow melt spinning (PFMS) is the only exception that we are aware of. Metglas, Inc uses PFMS to commercially fabricate alloys that enable power distribution transformers that are ultra-efficient, consuming little energy during operation. To the extent that our project lays a scientific foundation for PFMS sufficient to enable yet more efficient metallic glasses to be fabricated, society will benefit, as illustrated below using rapidly solidified alloys as an example. More thin metal fabrication in a single step -- aluminum foil. For single-step casting of aluminum foil, in contrast to the conventional multi-stage casting, direct energy savings alone translates to about 300 GW-hr/yr. Indirect benefits include the reduction of greenhouse gases, particularly, carbon dioxide. Estimates predict a yearly savings of about 250,000 tons of CO2 to the atmosphere. In addition, capital costs for manufacturing are reduced and productivity increased. Both climate and industry will benefit. More rapidly solidified fabrication using PFMS -- metallic glasses. Electricity from power plants is transmitted over long distances via high-voltage powerlines and stepped down by transformers. Energy losses in stepping down, even if small for each transformer, add up with the number of transformers in the network and the number of stepping operations. Conventional transformers are silicon-steel based, made by conventional multi-stage fabrication. Ultra-efficient transformers use novel amorphous alloys, made by rapid solidification. PFMS is the favored solidification technique but commercialization has yet to be achieved for the highest efficiency alloys because of gaps in our knowledge base. To get an idea of potential impact, it is estimated that if all the conventional (silicon-steel) power-distribution transformers in use today were suddenly replaced by the more energy-efficient (amorphous-alloy) transformers, worldwide CO2 emission would instantly decrease by 2.5% [1]. This corresponds to a yearly reduction of CO2 emissions by 170 million tons. For perspective, the Kyoto Protocol has a target of 6% reduction from 1990 levels of all green-house gases by 2012. In summary, transformer replacement alone would reach almost half the Kyoto goal by CO2 reductions alone. 1. Hasegawa, R & D Azuma (2008) "Impacts of amorphous metal-based transformers on energy efficiency and environment," J. Mag. Magnetic Mat. 320, 2451-2456.
