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M.Sc. Tim Storch
Lehrstuhl Werkstoffwissenschaft
Institut für Werkstoffe
Fakultät für Maschinenbau
Ruhr-Universität Bochum
Universitätsstr. 150
44780 Bochum

Gebäude ICFO, Ebene 04, Raum 341
+49 (0)234 32-15700
+49 (0)234 32-14235
Activities: Research Assistant
On the influence of σ-phase on the thermodynamic, kinetic and mechanical properties of polycrystalline superalloys.
As part of his PhD thesis, Tim Storch is doing research on the transfer project T6 of the "Sonderforschungsbereich" SFB/TR 103, which was established in collaboration with the industrial partner VDM Metals International. In project T6, work is carried out on a polycrystalline Ni-based superalloy, which is provided by the industrial partner and a development of the commercially available alloy VDM® Alloy C-264. Targeting to improve the creep properties, the Ti+Al sum (increase of the γ' volume fraction and the W concentration (slowing down particle coarsening) were increased compared to the predecessor alloy. However, the topologically close-packed σ-phase was also stabilized in this process. This complex structured TCP phase is mainly discussed in the literature as detrimental to the mechanical properties, whereas positive effects are also reported for small amounts of this phase. Nevertheless, these investigations were carried out on commercially available alloys with low σ-volume fractions (< 2 %).
Therefore, the transfer project T6 is addressing the question of what influence the σ-phase has on the mechanical properties. For this purpose, starting from the precipitation-hardened state, two model microstructure are set up which contain different σ-phase fractions (up to 6 %), while keeping the
γ/γ'-microstructure constant. Ongoing, different mechanical tests such as creep tests, high-temperature tensile tests or fatigue tests are carried out on these two microstructural states.
In addition, Tim Storch is working on a thematically related project funded by the "Deutsche Forschungsgemeinschaft" (DFG) dealing with the kinetics of the σ-phase in Ni-based superalloys. During precipitation of the TCP phase, a γ'-fringe forming around the σ-particles was observed in a superalloy with 16 % volume fraction of γ'-phase. This presumably changes the morphology of the
σ-phase from globular to elongated precipitates along the grain boundary.
Therefore, in the research project, Ni-based superalloys with the same chemical composition of the
γ-matrix - in order to keep the driving force of σ-phase precipitation constant - and different γ'-volume fractions (16 %, 8 % and 0 %) are produced. Then, the precipitation kinetics, particle density and growth of the σ-particles are systematically studied by microscopy.

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