Kinetics of Nonequilibrium Phase Transitions Initiated in Melted Nano- and Microsystems by a Bulk Heat Source

The paper presents a kinetic model of nonequilibrium phase transitions initiated in melted nano- and microsystems by a bulk heat source. The model allows for thermodynamic fluctuations of the order parameter as an important factor in the vicinity of a critical transition point, particularly when such systems reach absolute instability. Our research results suggest that such a nonequilibrium phase transition in a small-sized particle can proceed in two modes. At low heating rates, the system starts melting on its free lateral surface due to a critical fluctuation of the arising new phase there. The process develops toward the center as switching waves which transform the system from its metastable crystalline state to a stable liquid state. The volume of the system is overheated by 50 K. At high heating rates, local overheating regions with a temperature above 270 K arise in the crystal volume. These regions are unstable to infinitesimal fluctuations of the liquid phase and provide melting in the particle volume. The temperature and order parameter fronts arising on the free surface and in the volume travel fast and merge with each other.