Scuffing Resistance of Carburized Gear Steel with Laser-cladded Ni-based Composite Coatings

• • Laser-cladded NiCr20-3%ZrO2-1%MoS2 coatings on 18CrNiMo7-6 gear steel achieved a hardness of 690–730 HV0.1 and a thickness of ~1.2 mm, matching carburized case properties; this enables direct replacement or repair of hardened surfaces without compromising load-bearing capacity. • • Scuffing load capacity improved by 94.4% for tempered substrate, 61.3% for carburized substrate, and 50.7% for damaged repaired samples compared to uncladded carburized baseline; these gains are attributed to reduced friction coefficient from the self-lubricating MoS2 and ZrO2 phases, delaying critical failure under high contact loads. • • The laser cladding process induced HAZ transformations: tempered steel formed lath martensite and lower bainite near the coating and spheroidized structures in the lower HAZ; carburized steel developed coarse acicular martensite at the top, refined middle, and troostite at the bottom, with overall temper softening—these microstructural changes must be managed to avoid premature failure. • • Failure mechanisms differ: uncladded carburized samples formed a thin martensitic white layer causing rapid crack initiation and spalling; cladded samples exhibited deeper crack propagation and larger spallation, while repaired samples failed at the bonding interface due to poor adhesion, resulting in localized coating detachment—highlighting the need for improved interface engineering in repair applications.