BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Memento EPFL// BEGIN:VEVENT SUMMARY:The Icosahedron in Materials Science DTSTART:20150518T131500 DTEND:20150518T141500 DTSTAMP:20260925T054604Z UID:1795cec0161383a2b4142757802449af5675a59769aade4bb88eecad CATEGORIES:Conferences - Seminars DESCRIPTION:Prof. Michel Rappaz\, Institute of Materials\, EPFL\nThe icosa hedron\, a regular polyhedron with 12 vertices\, 20 triangular facets and 30 edges\, plays an important role in materials science. In the 1950’s a lready\, Frank postulated that atoms in the liquid may exhibit an icosahed ral short range order (ISRO) symmetry\, which could explain the large unde rcoolings measured by Turnbull in close-packed metals. ISRO was later conf irmed by X-ray diffraction measurements on levitated droplets. In the 1960 ’s\, Ino explained the dark-field images of nanoparticles by the fact th at they are made of 20 (or 5) fcc tetrahedra packed in multi-twinned icosa hedra (or decahedra) exhibiting low-energy {111} external planes. In the 1 980’s\, Shechtman et al discovered quasicrystals (QC) in Al-Mn alloys wh ich exhibit a 5-fold symmetry typical of the icosahedron\, but without tra nslation symmetry.\nAfter reviewing these interesting past discoveries\, w e will see how recent results[1\,2] indicate that nucleation of the fcc ph ase in certain liquid metallic alloys can be mediated\, rather than preven ted\, by the formation of icosahedral QC’s in the melt. QC’s can easil y nucleate in the melt because of their similarity with ISRO postulated by Frank\, with an associated very low interfacial energy. After some growth \, QC’s then act as precursors for the formation of the fcc phase via tw o mechanisms that will be discussed in this presentation: heteroepitaxy on QC facets or peritectic transformation of the outer layer of QC’s[3]. S uch a QC-mediated nucleation mechanism of the fcc phase\, which tends to r ule out standard homogeneous nucleation theories\, shares similarities wit h nucleation of precipitates in solids via intermediate metastable phases such as Guinier-Preston zones.\n[1] G. Kurtuldu\, Ph. Jarry and M. Rappaz\ , Acta Mater. 61 (2013) 7098.\n[2] G. Kurtuldu\, A. Sicco and M. Rappaz\, Acta Mater. 70 (2014) 240.\n[3] M. Rappaz and G. Kurtuldu\, J. Metals (201 5)\, to appear.\nBio: After a PhD in solid state physics (1979) at the Eco le Polytechnique Fédérale de Lausanne (EPFL) and a post-doc at Oak Ridge National Laboratory\, Michel Rappaz joined the Institute of Materials of EPFL in 1981. He was nominated Adjunct Professor in 1990 and Full Professo r in 2003.\nHis field of research has been focused on phase transformation s and solidification\, in particular the coupling of macroscopic aspects o f heat and mass transfer with microscopic aspects of microstructure and de fect formation. His group has developed several new modelling approaches a nd tools\, such as cellular automata and granular models of grain structur e formation\, models for microporosity and hot tearing formation in castin gs. Some of them have been commercialized by a spin-off company founded by his group in 1991 (Calcom SA)\, now part of the French company ESI. His a ctivity also encompasses many fundamental aspects of nucleation\, growth k inetics and phase/morphology competition in metallic alloys. Michel Rappaz initiated in 1992 an annual postgraduate course on solidification which h as been attended by more than 800 participants from all over the world.\nM ichel Rappaz has received several awards\, in particular the Mathewson co- author award (1994) and author award (1997) of the American Mineral\, Meta ls and Materials (TMS) society\, the Koerber foundation award with Profs Y . Bréchet and M. Asbby (1996)\, the Sainte-Claire Deville Medal (1996) an d the Grand Medal (2011) from the French Materials Society\, the Bruce Cha lmers Award of TMS (2002)\, the Mc Donald Memorial Lecture award of Canada (2005)\, the FEMS European Materials Gold Medal (2013) and the Brimacombe Prize of TMS (2015). He is a highly-cited author of ISI\, a fellow of ASM \, IOP and TMS\, and has co-authored more than 200 publications and two bo oks. LOCATION:MXF 1 https://plan.epfl.ch/?room==MXF%201 STATUS:CONFIRMED END:VEVENT END:VCALENDAR