Surface Engineering of Cu-Zn Alloys via Femtosecond Laser Processing

This review presents a comprehensive analysis of the physicochemical mechanisms underlying surface engineering of Cu–Zn alloys through femtosecond laser processing. It focuses on the coupled evolution of laser-induced plasma formation, selective ablation, nonequilibrium Zn redistribution, and plasma-assisted oxidation. Experimental and theoretical evidence indicates that ZnO formation cannot be explained by gas-phase reactions or surface oxidation alone, but results from the interplay of plasma processes, diffusion-controlled Zn redistribution, and heterogeneous oxidation under nonequilibrium conditions. A plasma–surface–diffusion framework is employed to interpret these coupled processes, linking selective Zn redistribution, plasma-assisted oxidation, and ZnO formation within the laser-modified surface layer. The review discusses ZnO evolution, including the influence of supersaturation, defects, and relaxation times, and highlights the effects of laser-induced structuring on reaction kinetics, energy redistribution, and mass transport. Comparison with plasma-assisted and gas-phase ZnO synthesis demonstrates common kinetic stages while emphasizing the localized and transient nature of femtosecond laser processing. This integrated interpretation provides a mechanistic basis for controlled ZnO formation. Overall, ZnO formation on Cu–Zn alloys is interpreted through a multiscale physicochemical approach integrating nonequilibrium electron excitation, plasma evolution, Zn redistribution, heterogeneous oxidation, and surface morphology, providing a framework for the rational optimization of laser-functionalized brass surfaces.