Friction transition and wear behavior of grid-textured surfaces fabricated by laser-directed energy deposition

This study proposes a directed energy deposition (DED)–grinding hybrid process for fabricating grid-type lubricant pocket patterns on high-hardness tool steel surfaces and evaluates its tribological implications under starved boundary lubrication. Grid patterns with spacings of 1.2, 1.5, and 1.8 mm were formed on an AISI M4 DED layer deposited on an SKD11 substrate, with the pocket depth uniformly controlled to 50 ± 0.5 μm by surface grinding. Pin-on-disc tests (400 N, PAO 1, starved boundary lubrication) revealed that friction transition and wear behavior strongly depended on the effective pocket area ratio ( A net ), which was reduced from the nominal design due to residual particles inside the pockets. The largest spacing condition ( A net ≈ 20.8%) exhibited the most delayed film breakdown ( t fb = 4192 ± 485 s) and the highest wear resistance. Surface observations indicated that sufficiently large effective pockets promoted preferential trapping of oxide-rich third-body debris, suppressing debris re-entrainment and stabilizing asperity contact. These results demonstrate that DED-based surface patterning is a viable manufacturing strategy and highlight the importance of controlling effective pocket geometry to regulate third-body behavior and friction transition in additively manufactured textured surfaces.