International research project investigating effects of gravity on aluminium-based alloy solidification

The European Space Agency (ESA) has chosen a UCD researcher to spearhead the XRMON project, a multidisciplinary, international collaboration investigating the effects of gravity on aluminium-based alloy solidification using real-time, in-situ X-radiography.

In addition, the university has been chosen as the lead partner in the next phase of the research, which involves carrying out an experiment in which an aluminium alloy will be solidified in zero gravity on a sounding rocket flight – a rocket carrying instruments designed to take measurements and perform scientific experiments.

This is a first both for Ireland and UCD, as it is the first time an Irish scientific team has led such a project, which is funded under the ESA's Microgravity Applications Promotion (MAP) programme.

Dr David Browne, from the UCD School of Materials Science and Engineering will lead the XRMON consortium until 2018. His postdoctoral researcher Dr Andrew G Murphy will also be a member of the XRMON team.

A rocket containing the experiment is due to launch from Kiruna, Sweden, in October this year. Dr Browne and Dr Murphy will be controlling the experiment remotely from the Swedish Space Corporation.

Approximately 75 seconds after launch the sounding rocket payload will enter a free-fall period lasting around six minutes, resulting in zero-gravity conditions inside the experiment module, thus enabling observations of metal solidification processes, without the normally significant effects of gravity.

All metal solidification (casting) processes are subject to the effects of gravity. Computer modelling of these processes is difficult, because gravity cannot be controlled anywhere on earth. But by conducting experiments in microgravity conditions, a greater understanding of the effects of gravity on solidification can be gained.

Dr David Browne explained that the aim of the research project is to uncover scientific detail on how metal alloys solidify from the liquid state. He said the processes of solidification are of relevance to industrial casting processes.

"During such freezing of alloys, solid specks appear in the liquid and then grow as dendrites – looking essentially like snowflakes. Gravity affects what happens to these dendrites on earth because it forces them to move – for example around a mould in natural convective flow, or straight up or down in the remaining liquid, according to buoyancy forces which cause either floating or settling."

"This makes the physics of alloy solidification hard to predict. We can make the science easier if we can extract the flow due to gravity, but this is only possible for any reasonable period of time in zero-gravity conditions achievable in space.

"This is where the ESA comes in, as they have a sounding rocket programme which achieves zero gravity on board for up to 10 minutes," he added.

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