The wet tribological behaviors of doughnut patterns laser-textured on DF2 tool steel under different loading conditions

Circular spot was irradiated by a Nd:YAG laser under a particular operational setup producing crater-like (or doughnut-like) feature, which was anticipated to generate favorable hydrodynamic effects in wet lubrication condition. It was used to ablate the pattern in either an in-line (IN) or staggered (ST) arrangement on DF2 tool steel plates. The irradiated DF2 tool steel plates with patterns of either in-lined (IN) or staggered (ST) spot arrangement, together with their nonpatterned (NP) counterparts, were respectively slid reciprocally against ASSAB 17 steel pin immerging in a basin containing Shell Tellus T32 lubricant and under loading of 400 N, 700 N, and 800 N, respectively. Test results showed the tribological behaviors of the three types of surface textures getting poorer with the increase of loading. Study demonstrated that ST gave superior nominal tribological characteristics, followed by IN and NP. Relevant mechanisms were also elucidated by analyzing SEM micrograph, PGI graphic, and Talysurf surface profiles of surface morphology, and EDX spectra. The existence of hydrodynamic effect of the ablated spot was simply verified by a simplified numerical simulation.