Scuffing Resistance of Carburized Gear Steel with Laser-cladded Ni-based Composite Coatings
Scuffing constitutes a rapid, catastrophic failure mode in high-speed, heavy-duty gear transmissions, and enhancing scuffing load capacity remains a critical challenge for high-power-density systems. This study investigates the feasibility of laser cladding to improve scuffing resistance and repair scuffed tooth surfaces on 18CrNiMo7-6 gear steel. Three substrate conditions—tempered, carburized, and carburized with pre-induced scuffing damage—were coated with NiCr20-3%ZrO2-1%MoS2 (mass fraction) via a MobiMRO-2 laser cladding system with synchronous powder feeding. The cladded layer, approximately 1.2 mm thick, exhibited a dendritic, cellular, and irregular particulate microstructure with hardness of 690–730 HV0.1, comparable to the carburized case. Laser cladding induced significant heat-affected zone (HAZ) transformations: tempered steel formed lath martensite and lower bainite near the coating, with spheroidized structures in the lower HAZ; carburized steel developed coarse acicular martensite at the top, refined structures in the middle, and troostite at the bottom, with overall temper softening. Scuffing tests using a two-disc rolling contact rig under step-wise loading revealed that cladded tempered, cladded carburized, and repaired samples achieved 94.4%, 61.3%, and 50.7% increases in scuffing load capacity, respectively, relative to uncladded carburized baseline. This enhancement stems from increased hardness and the self-lubricating effect of the coating, which reduced interfacial friction coefficient and delayed critical failure. Failure analysis showed that the cladded layer altered crack initiation and propagation paths, significantly raising the critical failure load. The repaired samples, however, exhibited poor bonding at the original damage interface, leading to localized coating detachment. These findings confirm laser cladding as an effective method for enhancing gear scuffing resistance and repairing scuffed surfaces, providing experimental and theoretical support for surface strengthening and damage repair.