Synergistic reinforcement of 38MnVS6 steel via soft–hard gradient laser cladding: Microstructural optimization and tribological behavior

Abstract

Severe adhesive and fatigue wear of steel piston top ring grooves under high-temperature, high-pressure, and boundary-lubricated conditions significantly compromise engine efficiency and durability. To address this, a novel Fe-based functionally graded coating (FGC) featuring a soft–hard architecture was fabricated on 38MnVS6 steel via laser cladding. This design aims to synergize high surface load-bearing capacity with superior interfacial toughness. Detailed microstructural characterization reveals a gradient transition from a Cr/C-rich hard layer, reinforced by M₇C₃ carbides and submicron grains (0.87-0.98 μm), to a ductile Fe-based solid-solution soft layer. The hard layer attains an average hardness of 616HV—approximately 2.3 times that of the substrate—effectively resisting plastic deformation. Under rigorous boundary lubrication tests at 230°C, the FGC demonstrates superior tribological stability, reducing the wear volume by more than one order of magnitude compared to the substrate. The dominant wear mechanism notably shifts from severe adhesion and delamination to mild abrasive and limited oxidative wear. These findings elucidate the crucial role of the gradient microstructure in suppressing high-temperature wear, providing an effective route for the surface strengthening and remanufacturing of critical engine components.