Abstracts 175

P98 Severe Plastic Deformation as a Tool to Produce Nanocrystalline Metals *) 1) M.Zehetbauer, E.Schafler, L.Stegelmann, H.P.Karnthaler, B.Mingler 2) H.P.Stuwe, P.Les, R.Pippan, T.Hebesberger 1) Institute of Materials Physics, University, 2) Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Leoben, Austria Recent research has shown that nanocrystaDine (NC) metals can be produced by severe plastic deformation (SPD) provided certain deformation modes will be applied. In comparison to all previous methods to produce NC metals, this technique will offer important advantages as concerns minimization in pore size and maximisation in sample size. First systematic investigations show that the hydrostatic pressure component rules the final grain size while the number of deformation axes seems to be responsible for their shape. As compared to conventional large strain deformation techniques, those of SPD yield about 1.2-3 times higher strength values which are reached at 4-30 times higher strains. Moreover, SPD yields markedly higher densities of deformation induced lattice defects which also appears to be a consequence of the enhanced hydrostatic pressure restricting atomic lattice diffusion. *) Joint Project 12944-45 funded by the Austrian Science Foundation (EWJB

P99 AT0100307 K Silver precipitates in a Cu matrix studied by HRTEM methods B. Mingler and H. P. Karnthaler Institute of Materials Physics, , Boltzmanng. 5, A-1090 Vienna A Cu-3.5 at.%Ag alloy combines high strength with high heat conductivity; the combination of these properties is of special interest for technical applications. In this alloy semi coherent Ag precipitates occur that govern the mechanical properties since Ag is hardly soluble in Cu even at high temperatures. High resolution transmission electron microscopy (HRTEM) images show that the interfaces between the Ag precipitates and the Cu matrix are parallel to (111) Cu planes. To compensate the difference in the lattice constants of Ag and Cu (0.409 and 0.362 nm, respectively) the presence of periodically arranged misfit dislocations is needed with a periodicity of about 9 atomic spacings on the Cu side. Some of these precipitates are in twin orientation with respect to the corresponding lattice planes in the Cu matrix. Both the twin plane and the interface are parallel to {111} planes. This orientation relationship is in contrast to results of previous investigations stat! ing that the interface is tilted by 15° to the twin plane. Financial support of the "Hochschuljubilaumsstiftung der Stadt Wien" is acknowledged.