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Lecture

### Effect of precipitation on grain boundary diffusion in an Al-based alloy

Wednesday (28.09.2016)
16:00 - 16:15
Part of:

Precipitation phenomena affect the kinetics of diffusion in the surrounding matrix. The present study is focused on the effect of $\rm{Al}_{3}\rm{Sc}$ precipitates on grain boundary diffusion in an Al-based AA5420 alloy (Al-4.6Mg-0.64Mn-0.2Sc-0.09Zr-0.2Ti-0.08Fe-0.02Si). Different states in polycrystalline material were prepared by a combination of severe plastic deformation and heat treatments and the radioisotope ${}^{57}\rm{Co}$ was employed as a sensitive probe of the given grain boundary state. The results suggest that the Co diffusion rates can intimately be coupled to the precipitation behavior of $\rm{Al}_{3}\rm{Sc}$ established via mechanical-thermal treatment. In fact, the Co diffusion coefficients are first decreasing with increasing precipitate size and approach a minimum at their average size of about 20 nm, which is probably related to maximal elastic stresses around the precipitates. As the precipitates grow further, the diffusion coefficients begin to increase due to a loss of coherence accompanied by a change in the chemical composition and/or formation of core-shell structures and a reduction of stresses around the precipitates. In order to explain the experimental findings the effect of stress and strain fields around precipitates on the Co diffusion coefficients is analyzed employing density functional theory.

Financial support by DFG via SPP1713, the projects DI 1419/7-1 and HI 1300/8-1 is gratefully acknowledged.

Speaker:
Bengü Tas Kavakbasi
University of Münster
Additional Authors:
• Vladislav Kulitckii
Belgorod State University, Russia
• Ankit Gupta
Max-Planck-Institut für Eisenforschung, Düsseldorf, Germany
• Yulia Buranova
University of Münster, Germany
• Biswanath Dutta
Max-Planck-Institut für Eisenforschung, Düsseldorf, Germany
• Dr. Tilmann Hickel
Max-Planck-Institut für Eisenforschung, Düsseldorf, Germany
• Dr. Sergiy V. Divinski
University of Münster, Germany
• Prof. Dr. Gerhard Wilde
University of Münster, Germany