HEAT TRANSFER, PHASE CHANGE, AND THERMOCAPILLARY FLOW IN FILMS OF MOLTEN METAL ON A SUBSTRATE

Abstract

A mathematical model has been developed for heat transfer and fluid flow in thin films of molten metal during nanosecond pulsed laser irradiation. Heat conduction in the substrate is modeled using the finite-difference approach, while description of heat transfer and viscous flow in the film is based on the assumption of the large ratio of laser beam radius to film thickness and involves numerical solution of a partial differential equation for the thickness. The model includes the highly nonlinear dependence of evaporative flux on local interfacial temperature and positive disjoining pressure due to free electrons in the metal. Thermo-capillary stresses which result from radially nonuniform heating are identified as the main mechanism of removal of liquid metal from the irradiated area. Characteristic times of the process, as well as shapes of the molten surface, agree with experimental observations.