ESTIMATION OF THE MELTING FRONT VELOCITY IN IRON EXPOSED TO A PICOSECOND LASER PULSE

10.25712/ASTU.1811-1416.2026.02.004

Abstract

The kinetics and mechanisms of melting of an α-iron single crystal induced by a single picosecond laser pulse were studied using molecular dynamics simulation. To simulate rapid surface heating, an approach was used in which the initial temperature distribution was specified in accordance with the solution of the heat conduction equation, taking into account the thermophysical properties of the material and the irradiation parameters. The key variable factor determining the thermal state of the system was the energy density of the laser pulse. A computer experiment detected the formation of a two-phase "melt-solid" system and studied its evolution. Using a common neighbor analysis algorithm and subsequent construction of an isosurface based on a scalar field of local structural ordering, the position of the interphase boundary was identified at various points in the simulation time. The analysis revealed the simultaneous occurrence of heterogeneous and homogeneous melting mechanisms, which directly indicates that the crystal lattice has reached a significant superheated state. Based on an analysis of interphase boundary displacement, the dependence of melting front velocity on superheating was determined over a wide range of irradiation power densities. It was found that at superheats above 300 K, the front velocity reaches values ​​on the order of several hundred meters per second. It was shown that the resulting dependence is satisfactorily described by the modified Wilson-Frenkel kinetic model, confirming the applicability of this phenomenological approach to describing ultrafast phase transitions. The obtained quantitative data can be used to verify continuum models and optimize precision laser micromachining and ablation modes, where control of the depth and morphology of the melted zone is critical.