Prof Lorenz Ratke - DLR, Germany
Lorenz Ratke is Professor for Metal Physics at the RWTH Aachen University and head of the research group "Polyphase solidification" at the Institute of Materials Physics in Space at the German Aerospace Center, DLR in Cologne. He received his diploma in Physics at the University of Münster 1975 and his PhD in Metal Physics from the RWTH Aachen University 1979. Professor Ratke held positions at the Vereinigte Aluminium Werke Bonn, the Technical University in Clausthal, the Max-Planck-Institute for Metals Research in Stuttgart and visiting positions at the Northwestern University in Evanston, USA, the University of Miskolc, Hungary and the University of Iowa, USA. He has received the Georg-Sachs-Award of the German Society of Materials, Acta Metallurgica et Materialia Outstanding Paper Award, Senior Scientist Award of the DLR, the Innovation Award of the City of Cologne and the Bavarian State Innovation Award. He has received the Doctor honoris causa from the University of Miskolc 2007. He has published over 300 papers in the areas of corrosion, powder metallurgy, in-situ composites, polyphase solidification and coarsening of microstructures.
Phase separation in liquid immiscible alloys: from fundamentals to applications
Institute of Materials Research, German Aerospace Center DLR, Germany
The solidification of alloys whose phase diagrams exhibits a miscibility gap in the liquid state commonly leads to a microstructure with an extremely large macro-segregation. Typically the elements of such alloys have both a very large melting point and density difference promoting gravity induced segregation on passing the miscibility gap during cooling. Such alloys like Al-Pb and Al-Bi promise to be excellent candidates for self-lubricating bearings, since a soft phase can be embedded into a tough, abrasive wear resistant matrix automatically on solidification, if it would be possible to control the liquid-liquid phase separation appropriately. Unfortunately it turns out that besides gravity many other effects or forces influence largely the microstructure evolution.
The classical concept of microstructure evolution in cast immiscible alloys would simply start with nucleation of a liquid minority phase, its growth and sedimentation in the gravity field terminated mostly by the monotectic reaction. Such a concept is far from being complete and neglects important effects, like coagulation of droplets, interfacial tension driven fluid flow and drop motion, interaction of drops with the monotectic reaction front, their pushing and engulfment and small scale convective patterns ahead of the front and many more. The lecture will give an overview about the research of the last four decades on phase separation in immiscible alloys, the essential breakthrough made by first experiments in microgravity decades ago and how systematic experimental and theoretical research revealed not only the essential mechanisms but also lead to a new industrial processes such that the dream that started 100 years ago with a British patent on immiscible alloys could become true, namely making from Al-Pb- or Al-Bi-base alloys excellent, high performance bearings for car engines.