Microstructure and Impact Resistance of ‘Sandwich’ Composite Coating by Laser Cladding

Because of harsh working conditions, the tooth surface of the active wheel gear ring experiences severe corrosion and wear under high-impact loads. Current tooth surface reinforcement techniques do not substantially increase impact and corrosion resistance. Hence, this study designed a ‘sandwich’ composite coating with an interfacial layer, a toughening layer and a wear-resistant layer on the ZG42CrMoA material. The coating comprises γ-Ni, M₂₃C₆, MoNi, MoNi₄, Ni₃B, WC and W₂C. The interface layer removes pores and inclusions in the substrate, thereby creating a strong metallurgical bond and fortified coating-substrate adhesion. The toughened layer, enriched with Mo at grain boundaries, impedes Cr diffusion. Moreover, tungsten carbide (WC) nanoparticles refine the grain structure, strengthen grain boundaries, limit dislocation slip and improve impact resistance. The toughened layer absorbs energy via plastic deformation, further augmenting impact resistance. As a result, the composite coating exhibits better impact toughness than high-frequency quenched specimens. Impact tests and finite element analysis demonstrate that the composite coating’s maximum compressive stress is 253.11 MPa, compared to 288.63 MPa for the high-frequency quenched layer. Due to its high hardness and brittleness, the high-frequency quenched layer endures restricted plastic deformation under the impact, developing stress concentration zones that lead to cracks and fracture and lowered impact resistance. Alternatively, the γ-Ni solid solution in the composite coating provides good toughness, allowing more plastic deformation, decreased stress, alleviated stress concentration and significantly improved impact resistance.