Dresden 2009 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 29: Diffusion and Point Defects II
MM 29.4: Talk
Wednesday, March 25, 2009, 12:45–13:00, IFW D
Decomposition phenomena in Al alloys investigated by positron annihilation at low temperatures and XAFS — •Benedikt Klobes1, Matz Haaks1, Karl Maier1, Christiane Rieke1, and Torsten Staab2 — 1Helmholtz-Institut für Strahlen- und Kernphysik, Nußallee 14-16, D-53115 Bonn — 2Fraunhofer-Institut für Silicatforschung ISC, Neunerplatz 2, D-97082 Würzburg
The decomposition phenomena occurring in AlCu(Mg) and AlMgSi alloys greatly affect their mechanical properties. Usually, these alloys are solution heat treated and quenched. During post-quench ageing metastable phases are formed which hinder dislocation movement and, thus, constitute the industrial use of these alloys. However, the early stages of decomposition involving agglomerates of few alloying atoms are hard to access experimentally. Therefore, an understanding of the evolution of these stages has not yet been established. Positron annihilation spectroscopy (PAS) has proved its usefulness for the investigation of Al alloys in the last decades and, recently, its sensitivity to the first stages of decomposition. Usually, positrons are attracted by open-volume defects, but utilising the higher positron affinity of nearly all alloying elements in comparison to Al it is possible to probe even defect-free coherent agglomerates by measuring the low temperature dependence of PAS observables. Mainly studying the positron lifetime between 40 and 300 K we attempt to follow the evolution of first agglomerates with and without structural vacancies in AlCu(Mg) and AlMgSi alloys. These results will be correlated with measurements of the x-ray absorption fine structure (XAFS).