M6 Nickel-base superalloys
| Prof. Dr. Uwe Glatzel | Dr. Michael Fleck |
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| uwe.glatzel@uni-bayreuth.de | michael.fleck@uni-bayreuth.de |
Nickel-base superalloys belong to an important class of applied materials, which show a strong coupling of thermo-chemical and thermo-mechanical states in the sense of the DFG priority program SPP1713. These materials have various applications at elevated temperatures, especially in stationary gas turbines and aero-plane engines. The main strengthening mechanism, which makes these alloys applicable for high temperatures is particle strengthening by coherent precipitations. For high temperature wrought alloys, such as Inconel 718, the main precipitation strengthening phase is the so-called γ”-phase, which is an ordered tetragonal phase. Despite of it’s technological importance this phase is found to be meta-stable, and does not contribute to the equilibrium phase diagram. Therefore, it is very important to consider the kinetics of microstructure evolution in this class of alloys.
The aim of the project is to study the growth and coarsening of meta-stable γ”-particles under external thermo-mechanical loads. The respective γ/γ” microstructure evolution will be investigated in a joint approach using phase field simulations together with customized metallurgic experiments. In contrast to existing investigations on the Inconel 718 alloy, we will focus on γ” precipitation only. This is achieved by the consideration of the alloying systems, which do not contain γ’-building elements, such as Al or Ti, and thus will not show any further γ’ precipitation. The respective experimental samples will be processed out of carefully prepared single crystal casts, that are free of any grain boundaries, which provides a further focus on the physical mechanism of particle strengthening by coherent precipitations. We point out, that this mechanism involves a strong coupling between the materials solutal-chemistry and the thermo-mechanics of the microscopic phase structure. The resulting thermodynamic and elastomechanic description is coupled in the two directions:
- On the one hand, the γ/γ”-phase-structure of the material depends on the history of external mechanical loads, as, for instance, the application of different loads can lead to the selection of different orientational variants.
- On the other hand, the response of the material to loads depends on the phase-structure in two different respects: First the hardness and second the elastic stiffness.
The expected outcome of the project is two-fold: On the one hand, we aim to deepen the understanding of the elastic influences on the kinetics of γ”-precipitation growth and coarsening. On the other hand this phenomenon is considered using a joint experimental and simulation approach to question and develop the respective modeling approaches.