Time: 10:00 a.m.
Place: UHW 11/1102
Frank Stein, Department of Microstructure Physics and Alloy Design, Max-Planck-Institut für Eisenforschung, Düsseldorf, Germany
Laves phases form the largest group of intermetallic phases and are often quoted as the classical example for atom-size-controlled compounds. They have attracted much attention as possible materials for high-temperature applications since long. Within the inter-institutional research initiative "The nature of Laves phases" of the Max Planck Society, Laves phases in a variety of binary and ternary transition metal-based systems have been investigated aiming at an improved understanding of the stability and structure of these phases. Laves phases may crystallize in three different, closely related structure variants, which are the cubic MgCu2 type (C15), the hexagonal MgZn2 type (C14), and the hexagonal MgNi2 type (C36). Selected phase diagrams have been carefully re-investigated to study the co-existence of different Laves phase polytypes and the extension of their frequently very large homogeneity ranges. The composition dependence of the crystallographic parameters and the role of chemical disorder and site occupations are discussed showing the importance of intrinsic differences between the cubic and the hexagonal Laves phase polytypes. Finally, the dependence of the mechanical properties of single-phase Laves phase material on structure and composition will be presented revealing an unexpectedly strong effect of deviations from stoichiometry.