Involvement in two EU research programmes is helping to put Irish science into orbit. Experiments being developed by University College Dublin engineers will be blasted into space and carried on board the International Space Station to help improve our understanding of metal alloys, writes Dick Ahlstrom
"The main link between the two projects is space and in particular the International Space Station (ISS)," says Dr David Browne of the department of mechanical engineering at UCD.
"On board the space station the conditions are those of freefall, the centrifugal force is exactly equal and opposite to the gravity force. There is no net gravity," he says. This makes it a "unique environment" for the study of how molten alloys solidify in a mould, information that could help develop either better alloys or better metal casting methods, he adds. "Ultimately this could lead to improvements in processes on earth."
Casting metal seems a straightforward process, you pour liquid metal into a mould and wait until it solidifies. For a time however the mould will hold both solid metal at its edges and liquid towards its hotter centre. This sets up "circulation loops, natural convection", says Browne.
"This liquid flow has a very strong effect on the final solidified structure and its microstructure," he adds. "The microstructure in turn has a very strong effect on the properties of the casting." These convection effects don't occur without gravity however. Browne, his UCD group and the broader consortium are using the micro gravity available in space as a way to isolate the effects of natural convection by comparing castings done on earth with castings done on board the ISS.
The two programmes are known as CETSOL and IMPRESS and both involve large-scale collaborations with research partners in other states. The former looks at how micro gravity affects conventional metal alloy casting, particularly involving aluminium, says Browne. Organised and funded by the European Space Agency, UCD is working on computational modelling of how molten alloys crystallise and solidify.
"We are developing computational models of solidification," says Browne. Computer models will describe how crystal growth occurs in the solidifying casting. "Predictions from them will be used by our partners in the European consortium to design and build experiments for the space station."
The second, IMPRESS, is again coordinated by ESA but funded via the sixth Framework Programme for European Research. Here UCD is involved in two areas, computational modelling of the behaviour of specialist alloys and also the design of experiments for the ISS.
IMPRESS focuses on exotic materials known as "intermetallics". They behave like metals but also have characteristics akin to ceramics. They have a different crystal structure compared to typical metals, he says. They are harder, tougher and more temperature resistant than conventional metals, but can be brittle.
They are looking at titanium aluminide for use in turbine blades and nickel aluminide for use as catalysts. "It is related to the development of industrial processes which can successfully produce useful components from these intermetallic materials," says Browne.
"All three parts of our work are related to the solidification of these materials. The first two are related to casting processes. The third is related to the solidification of droplets of nickel aluminide intermetallic to form fine powders for use in catalysis, for example in hydrogen fuel cells."
The predictive element of UCD's contribution is important. It costs about $30,000 (€25,500) per kilogram to launch an experiment into orbit. Experiments must be chosen with great care to avoid wasting money.