Ephraim Schoof

Modelling of transient heat conduction with diffuse interface methods

We present a survey on different numerical interpolation schemes used for two-phase transient heat conduction problems in the context of interface capturing phase-field methods. Examples are general transport problems in the context of diffuse interface methods with a non-equal heat conductivity in normal and tangential directions to the interface. We extend the tonsorial approach recently published by Nicoli M et al (2011 Phys. Rev. E 84 1-6) to the general three-dimensional (3D) transient evolution equations. Validations for one-dimensional, two-dimensional and 3D transient test cases are provided, and the results are in good agreement with analytical and numerical reference solutions.

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.