Two-dimensional phase field crystal simulation of laser-induced recrystallization: A mechanism of grain-boundary phonon scattering and softening

In this article we present, as far as we know, the first numerical investigation of phonon relaxation in two-dimensional polycrystalline systems simulated with a multitimescale phase field crystal model. We first measure the phonon spectrum averaged over different polycrystalline configurations using thermal fluctuations to capture the rapid processes. We find two main peaks in the spectrum attributable, respectively, to dampening and softening of different wavelength phonons. In particular, it is shown that polycrystals have a phonon caging regime, a signature of amorphous materials. Subsequently, we report on a mechanism of grain-boundary melting resulting from the accumulation of phonon scattering. We find this behavior exhibited in both rapid temperature annealing of polycrystalline samples and from input of kinetic energy representative of rapid laser heating or hot-rolling. In the latter case, we theorize a rate relation between the maximally achieved liquid fraction as a function of the initial kinetic energy, defining a metastable activation energy that can be measured in experiments. We expect that the scattering mechanisms investigated in this work underpin grain-boundary melting and recrystallization processes encountered in rapid solidification experiments.