A systematic correlation study on process-structure-performance of iron-based gradient coatings by laser cladding for rolling mills

• Six-layer gradient coating with Ni content decreasing from 7.01% to 1.03% effectively eliminates interfacial stress concentration • Optimal laser power of 6500 W (2.955 J/mm linear energy) produces uniform equiaxed α-Fe microstructure with 18.7 μm grain size • Interface shear strength reaches 423.9 MPa, representing 86% improvement over single-layer coatings • Smooth hardness transition from substrate (250 HV) to working layer (700 HV) with 50-100 μm metallurgical bonding zone • Volume wear rate of 9.88 × 10⁻⁵ mm³/N·m achieves 24.6% improvement with predicted service life extension exceeding 230% To address the failure of roll coatings caused by interfacial thermal stress concentration, this study employed laser cladding technology to fabricate an iron-based functionally graded wear-resistant coating on 9Cr2Mo steel. A six-layer gradient structure with nickel content gradually decreasing from 7.01% to 1.03% was designed to eliminate interfacial abrupt transitions, mitigate stress concentration, achieve smooth transitions in mechanical properties, and significantly enhance bonding strength and wear resistance. Microstructural analysis revealed that the deposited layer primarily comprises α-Fe solid solution incorporating uniformly dissolved Cr and Mo elements, forming a 50-100 μm wide element interdiffusion zone with excellent metallurgical bonding. EBSD analysis showed uniform grain orientation distribution and weak texture intensity, providing a microstructural basis for superior mechanical properties. The gradient design effectively reduced thermal stress from 420 MPa to less than 200 MPa and the stress concentration factor from 1.84 to 1.15. Under optimal conditions 6500 W laser power), key performance indicators included: interface shear strength of 423.9 MPa (86% higher than single-layer coating of 227.8 MPa), smooth hardness transition from 250 HV (substrate) to 700 HV (working layer), volume wear rate of 9.88 × 10⁻⁵ mm³/N⋅m (24.6% lower than substrate), and stable friction coefficient ranging from 0.30 to 0.32. The primary wear mechanism was identified as abrasive wear. This research establishes quantitative relationships between process parameters, microstructure, and properties, providing theoretical foundation and technical support for industrial application of laser cladding in roller surface repair.