Non-Equilibrium Phase Change in Metal Induced by Nanosecond Pulsed Laser Irradiation

Abstract

Materials processing using high power pulsed lasers involves complex phenomena including rapid heating, superheating of the laser-melted material, rapid nucleation, and phase explosion. With a heating rate on the order of 109K/s or higher, the surface layer melted by laser irradiation can reach a temperature higher than the normal boiling point. On the other hand, the vapor pressure does not build up as fast and thus falls below the saturation pressure at the surface temperature, resulting in a superheated, metastable state. As the temperature of the melt approaches the thermodynamic critical point, the liquid undergoes a phase explosion that turns the melt into a mixture of liquid and vapor. This article describes heat transfer and phase change phenomena during nanosecond pulsed laser ablation of a metal, with an emphasis on phase explosion and non-equilibrium phase change. The time required for nucleation in a superheated liquid, which determines the time needed for phase explosion to occur, is also investigated from both theoretical and experimental viewpoints.

Hybrid atomistic-macroscale modeling of long-time phase change in nanosecond laser–material interaction

“…In recent years, thermal transport, phase change, thermal stress development and propagation, and nanoparticle formation in laser-material interaction have been extensively investigated. Xu et al [13] investigated femtosecond laser ablation of copper with the emphasis on the understanding of the mechanism of phase change during laser ablation and studied non-equilibrium phase change in metal induced by nanosecond pulsed laser irradiation [14]. The dynamics of plume formation and parameters of the ejected clusters in picosecond laser ablation has been studied by Zhigilei [15] using large-scale molecular dynamics simulations.…”

Laser-induced forward transfer of pure metals

“…The observed atomization in the form of a spray like ejection obviously results in a massive contamination the receiving substrate and is likely to be explained by the phenomena of explosive boiling [115]. This is strongly supported by the velocity and the temporal evolution of the observed spray ejection, as it shows many similarities to the ablation mechanism, as studied in detail by Zhigilei et al [116].…”

Research and application of surface heat treatment for multipulse laser ablation of materials

“…where P is the saturated vapour pressure, Pa; C s is the viscosity coefficient (~1) [10], N.s/cm 2 ; and m 1 is the particle mass of the target material, kg.…”