Physics of Interfacial Force-Driven Surface Evolution in Pulsed Laser Surface Melting

Abstract Pulsed laser surface melting (pLSM) is a powerful micro-scale surface engineering technique that enables modification of surface morphology via localized melting and re-solidification. However, predicting interface evolution during pLSM remains a challenge due to the transient and coupled nature of thermal transport, fluid flow, and interfacial forces at small spatial and temporal scales. To address this, a dimensionless multiphase model was developed using the level-set method to track the evolving interface during pLSM. The model incorporates temperature-dependent surface tension and solves the coupled momentum and energy equations under a pulsed laser heat source modeled using Beer–Lambert's law. The predicted evolved interface showed strong agreement with experimental results in interface deformation. A detailed force analysis confirmed that interfacial tension forces are the dominant drivers of melt pool dynamics and interface deformation. Sensitivity analysis identified the Capillary number, Marangoni number, and Peclet number as key dimensionless parameters influencing interface behavior, while other dimensionless numbers were found to be less significant. A novel dimensionless quantity called the Marangoni interfacial coefficient (ηM) was introduced to characterize the relative influence of tangential and normal interfacial tension forces. A nearly linear relationship was observed between ηM and peak-to-valley height (PVH), demonstrating its utility as a predictive metric. In addition, empirical scaling laws were derived to link PVH directly with process inputs. This study establishes a physically grounded modeling framework for understanding and controlling interface evolution during pLSM and provides a generalized foundation for process optimization in laser-based surface modification techniques.