Combined laser surface modification and texturing of austenitic stainless steel 304 for tribological applications

Tesis Energía y Ambiente (maestría) - Instituto Tecnológico de Buenos Aires, Buenos Aires - Karlsruher Institut für Technologie, Karlsruhe, 2024 "In the global effort to reduce greenhouse gas emissions and enhance energy efficiency, tribological optimization presents a promising solution. With this goal in mind, this study investigated the influence of combining laser surface texturing with reactive laser surface remelting on the tribological behaviour of austenitic stainless steel 304 (V2A). V2A pins were subjected to a two-step laser treatment process consisting of a modification in atmosphere, followed by smoothing in Argon. This treatment created a remelted surface layer with distinct linear textures. Three different textured patterns were generated this way. Lubricated, unidirectional, pin on disc sliding tests were conducted on the laser-treated specimens across a range of speeds to evaluate behaviour under various lubrication regimes. The impact of unintended material acquisition at the edges of the pins from the laser treatment was also investigated through three separate test series. Untreated V2A pins served as a reference point for comparison in each series. Analysis included generating Stribeck curves from friction data and examining the surfaces using optical, topographical, and electron microscopy. Results showed significantly reduced wear in all laser-treated samples compared to untreated references, primarily due to incorporation of oxygen during laser treatment, mitigating wear mechanisms such as adhesion. However, surface area also played a crucial role, with untreated samples performing better at high sliding speeds due to their larger real contact area and easier transition to full-film lubrication. Furthermore, the presence of an elevated edge significantly impacted friction behaviour, leading to consistently low friction with minimal speed dependence, attributed to the reduced and geometrically favourable contact area created by the edge."