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M: Metallphysik

M 20: Intermetallische Phasen I

M 20.1: Vortrag

Samstag, 5. März 2005, 09:15–09:30, TU H2038

Mechanical Spectroscopy of Fe-Al alloys with Al concentrations up to 26 at.%. — •A. Strahl¹, S.B. Golovina², I.S. Golovin², and H. Neuhäuser¹ — ¹TU-BS, Institut für Metallphysik u. Nukleare Festkörperphysik, D-38106 Braunschweig — ²TU-BS, Institut für Werkstoffe, D-38106 Braunschweig

Temperature and time dependent internal friction (mechanical spectroscopy) of quenched Fe-Al-C alloys has been measured monitoring the Snoek-type relaxation (jumps of interstitial carbon atoms) in dependence of Al concentration. With an increase of Al substitutes in iron, the Snoek type peak changes its shape in a few steps. In the range 3-8 at.% Al in iron the peak is clearly composed of two Debye-type peaks: the peak at lower temperature corresponds to the original Snoek peak; the peak at higher temperature is caused by jumps of carbon atoms on places with nearby Al atoms. Above a critical Al concentration the original Snoek peak practically vanishes: in that case the surrounding of a C-atom is changed from Fe atoms to a random or ordered mixture of Fe and Al atoms, increasing the carbon hopping potential, shifting the Snoek-type relaxation to higher temperatures, and increasing the peak widths; such a peak is recorded in intermetallic compounds Fe₃Al.

By isothermal annealing experiments at selected temperatures around the observed peaks the long-term kinetics of carbon jumps has been followed in some detail to evaluate parameters of the process of carbon atoms removal from the interstitial solid solution. The observation of two relaxation rates associated with the decrease of Snoek-type peaks in Fe-Al-C alloys corresponds to nucleation and growth of carbides.