Morphological instability induced by the interaction of a particle with a solidifying interface

TL;DR

This paper demonstrates that particles near a solidifying interface can induce morphological instability at lower velocities than traditional thresholds, depending on physical parameters and thermal gradient reversals.

Contribution

It introduces a new instability mechanism caused by particle-interface interactions, expanding understanding of solidification dynamics.

Findings

Instability occurs when particle-interface distance is below a critical value.

The critical distance depends on physical and processing parameters.

Thermal gradient reversal is key to the instability mechanism.

Abstract

We show that the interaction of a particle with a directionally solidified interface induces the onset of morphological instability provided that the particle-interface distance falls below a critical value. This instability occurs at pulling velocities that are below the threshold for the onset of the Mullins-Sekerka instability. The expression for the critical distance reveals that this instability is manifested only for certain combinations of the physical and processing parameters. Its occurence is attributed to the reversal of the thermal gradient in the melt ahead of the interface and behind the particle.