Laser surface treatment of WSC coatings for selective crystallization of the TMD phase

Low friction in WSC coatings—comprising a WS 2 phase embedded within an amorphous carbon matrix—relies on sliding-induced WS 2 crystallization, process that typically requires prolonged running-in periods. Laser treatments can alternatively induce WS 2 crystallization prior to sliding, without compromising the structural integrity of the amorphous carbon matrix. However, current laser processing approaches are often imprecise and lack systematic optimization of the process parameters, as most research focuses on material ablation and topography modification, rather than structural transformations. This study systematically optimized the laser treatment of WSC coatings (~50 at. % C) under near-ideal conditions (WSCIR1-WSCIR3) to identify key variables and thresholds governing WS 2 phase crystallization and amorphous carbon graphitization. We adjusted laser parameters—average power, pulse duration, and repetition rate—and refined derived quantities such as energy per pulse, fluence, and power density. Geometrical, structural, and mechanical changes to the WSC coatings were then analyzed using optical microscopy, profilometry, ball cratering, Raman spectroscopy, X-ray diffraction, and nanoindentation. Increased laser exposure darkened and expanded the dimensions (diameter, height, depth) of the treated zones, and enhanced WS 2 crystallization—while maintaining coating hardness and elastic modulus due to minimal amorphous carbon graphitization. Our findings establish critical thresholds and present a precise, scalable pathway for engineering WSC coatings, potentially eliminating the need for extended running-in periods. • Fiber laser treatment modifies the structural properties of WSC coatings. • Identified thresholds for WS 2 crystallization and amorphous carbon graphitization. • Profilometry, Raman, and nanoindentation confirm laser-induced changes. • Potential for improved tribological performance of WSC coatings from running-in.