Overview of In Situ X-ray Studies of Light Alloy Solidification in Microgravity

Gravity has significant effects on alloy solidification, primarily due to thermosolutal convection and solid phase buoyancy. Since 2004, the European Space Agency has been supporting investigation of these effects by promoting in situ X-ray monitoring of the solidification of aluminium alloys on microgravity platforms, on earth, and in periodically varying g conditions. The first microgravity experiment – investigating foaming of liquid metals – was performed on board a sounding rocket, in 2008. In 2012 the first ever X-raymonitored solidification of a fully dense metallic alloy in space was achieved: the focus was columnar solidification of an Al-Cu alloy. This was followed in 2015 by a similar experiment, investigating equiaxed solidification. Ground reference experiments were completed in all cases. In addition, experiments have been performed on board parabolic flights – where the effects of varying gravity have been studied. We review here the technical and scientific progress to date, and outline future perspectives. 1 School of Mechanical and Materials Engineering, University College Dublin, Belfield, Dublin 4, Ireland. 2 Institute of Applied Materials, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-MeitnerPlatz 1, D-14109 Berlin, Germany. 3 Technische Universität Berlin, Structure and Properties of Materials Department, Hardenbergstr. 36, D-10623 Berlin, Germany. 4 IM2NP & Université d’Aix-Marseille, Campus St-Jérome, Case 142, 13397 Marseille Cedex 20, France 5 Access e.V., Intzestrasse 5, D-52072 Aachen, Germany. 6 Deutsches Zentrum fur Luftund Raumfahrt (DLR), Institut fur Materialphysik im Weltraum, Linder Höne, 51147 Köln, Germany. 7 Institut for Fysikk, Norsk Teknisk-Naturvitenskapelige Universitet (NTNU), 7491 Trondheim, Norway. 8 Bundesanstalt für Materialforschung und –prüfung (BAM), FB 9.4 Weld Mechanics, Unter den Eichen 87, 12205 Berlin, Germany. 9 Physical Sciences Office HRE-UP, Science Department, Human Spaceflight and Robotic Exploration Directorate, ESTEC, European Space Agency, BP 299, 2200AG Noordwijk, The Netherlands. *corresponding author: [email protected]