On the Volume-Diffusion Governed Termination-Migration Assisted Globularization in Two-Phase Solid-State Systems: Insights from Phase-Field Simulations
Morphology of the constituent phase in a microstructure influences the mechanical properties of the materials similar to the chemical composition, crystal structure and volume fraction of the phases. Often to enhance the mechanical properties, heat treatment techniques that exclusively facilitate the morphological evolution without any phase transformation are adopted. In the present work, the mechanism and the kinetics of this morphological transformation governed by the inherent curvature-difference introduced by the shape, referred to shape instabilities, are analysed through phase-field simulations. By monitoring the temporal evolution of the elliptical plate, a finite three-dimensional structure associated with two-phase titanium alloys, it is observed that the transformation is dictated by the recession of the edges, or termination migration. It is identified that the elliptical structure transforms to a rod before assuming an ellipsoidal shape at the midpoint and ultimately, evolves into a spheroid. The results of this work are compared with the existing analytical approach and the deviations introduced by the geometrical approximations of the theoretical study are discussed. Furthermore, for the first time, it is shown that the hitherto assumed monotonic decrease in the driving force is interrupted by a series of ‘aberrations’ predominantly in the first half of the transformation, which intensifies with increase in aspect ratio. An analytical prediction which includes this non-monotonic evolution of the curvature is presented from the outcomes of the simulation.
PGKA thanks the financial support of the German Research Foundation (DFG) under the project AN 1245/1. This work was performed on the computational resource ForHLR II, funded by the Ministry of Science, Research and Arts of Baden-Wuerttemberg and the DFG. Authors acknowledge the primary guidance of Prof. Kumar Ankit and Dr. Avisor Bhattacharya.
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