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A phase-field study to explore the nature of the morphological instability of Kirkendall voids in complex alloys
The present research explores theoretical and computational aspects of the morphological instabilityof Kirkendall voids induced by a directed flux of vacancies. A quantitative phase-field model is coupledwith a multi-component diffusion model and CALPHAD-type thermodynamic and kinetic databasesto obtain a meso-scale description of Kirkendall void morphologies under isothermal annealing. Thematerial under investigation is a diffusion couple consisting of a multi-phase multi-component single-crystal Ni-based superalloy on one side and pure Ni on the other side. The flux of the fastest diffuser inthe superalloy, Al, towards the pure Ni causes a strong flux of vacancies in the opposite direction. Thisdirected flux of vacancies leads to morphologically instable growth of voids. Phase-field simulationsare performed in two (2D) and three dimensions (3D) to understand these instabilities, and the resultsare compared with experimental observations obtained by synchrotron X-ray tomography. Finally, thesimulation results are analyzed with respect to the Mullins–Sekerka linear stability criterion.