Effects of High Current Density Impulses on the Properties and Microstructure of Nickelbase Superalloys

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Objective of the intended research project is the analysis of the effect of high current impulses on microstructure and mechanical properties of nickelbase-superalloys. First investigations showed plastic deformation of two monocrystalline nickelbase alloys (SC-16 and CMSX-4) significantly below yield strength while exposed to a high current density impulse. Furthermore, the effect depended on the prior creep deformation degree of the material. Nickelbase-superalloy PWA-1480 deformed in the same way showed a significant change in dislocation arrangement and element distribution. Both effects indicate a kind of regeneration effect of creep deformed nickelbase-superalloys. This regeneration effect is to be analysed during the intended research project. In a first step, compression tests below yield strength and with supply of a high current density impulse are to be carried out for two different nickelbase-superalloys in initial and creep-deformed state. Afterwards, changes in dendritic and dislocation structure and element distribution will be analysed. To verify the study of these microstructural changes, an in situ analysis method will be introduced. Application of the high current density impulses on creep specimens and subsequent creep tests (at the Bundesanstalt für Materialforschung und -prüfung, Berlin) will be used to determine the influence on the creep behaviour. Additionally, aluminium bicrystals will be mechanically stressed during high current density impulses. Objective is the analysis of the influence of the current pulses on dislocation dynamics in face-centered cubic metals in general. Finally, a synthesis of the results of the microstructural and mechanical analyses as well as of the investigations on the dislocation dynamics will be used for a deeper understanding of the regeneration effects and its possible applications.