Micron NbC-reinforced Fe-based cladding coatings via EHLA: Microstructure and corrosion

To surmount the drawbacks of conventional laser cladding—including excessive heat buildup, low processing efficiency, and the agglomeration issue of nanoscale reinforcing phases, micron-sized NbC particles reinforced Fe-based cladding coatings were obtained via the Extreme High-Speed Laser Cladding (EHLA) technique. This study systematically investigated the influences of NbC particles content on phase transformation, grain refinement mechanisms, microhardness gradient distribution, and corrosion behavior. The results reveal the presence of an α-Fe phase and an Fe-Cr phase in the base cladding coating, as well as an additional NbC phase in cladding coatings modified with micron-sized NbC particles. The introduction of micron-sized NbC particles is associated with significant grain refinement, which is consistent with heterogeneous nucleation and Zener pinning effects, leading to a structural transition from coarse dendrites to highly refined equiaxed grains. At a NbC content of 6 wt.%, the cladding coating exhibits remarkable grain refinement relative to the unreinforced base cladding, achieving a mean microhardness of 613 HV 0.5 , 92% higher than that of the unreinforced counterpart (319 HV 0.5 ). However, excessive addition of NbC (9 wt.%) results in particle agglomeration and grain coarsening. Electrochemical tests indicate that incorporating NbC particles improves corrosion resistance, which is inferred to be associated with enhanced passive film stability based on electrochemical measurements. Immersion experiments indicated that the 6 wt.% NbC cladding coating demonstrates superior electrochemical stability, providing a high-efficiency and cost-effective technique for surface strengthening of mechanical components serving in corrosive environments.