Coarsening and growth of meta-stable gamma''-precipitates in Nickel-base Superalloys

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The aim of the project is to study phase field modelling approaches for the simulation of gamma''- precipitation in a Ni-base model alloy, assisted by respective experimental characterisations.The central goal is to investigate the predictive power of the phase field modelling approache with respect to the kinetics of gamma''- precipitation growthas well as subsequent coarsening under selected loading conditions.The experimental reference for the phase field predictions will be high quality experimental microstructure data, generated within the project. In corresponding experimental investigations, we plan to quantitatively measure the sizes and shapes of the gamma''- particles for a series of different samples, aged under selected loadings at different times, covering the whole time range from the initial precipitation growth right into the gamma''- coarsening regime.A primary goal of the project is to experimentally investigate the mechanism of precipitation hardening of gamma''- particles only, which is of high fundamental relevance for the understanding of the hardness in high temperature Ni-base wrought alloys such as IN718. In contrast to gamma'- particles, the gamma''- precipitates exist in three different orientational variants, leading to a quite complex coarsening behaviour under load. The elementary physical mechanisms behind the growth and subsequent coarsening of gamma''- particles involve a strong coupling between the materials solutal-chemistry and the thermo-mechanics of the microscopic phase structure.According to the goals of the Priority Programme, it is a scientific key goal of the project to push forward phase field modelling as a technique, which resolves this thermo-chemo-mechanic interplay on a microcopic level, towards a better practical usability in a metallurgical and materials scientific context.