Effect of boron gradient design on the microstructure and properties of laser-clad Fe-based coatings

This study investigated the effect of boron gradient design on the microstructure, microhardness, and wear properties of laser-clad Fe-based coatings on 45 steel substrates. Two coating systems were fabricated by laser cladding: a gradient coating with boron content progressively increasing from 1.6 to 6.0 wt% across four layers, and a uniform multilayer coating with constant 6.0 wt% boron content. Comprehensive characterization revealed that the gradient coating exhibited a controlled evolution of boride morphology from networked eutectic to clustered-shape and finally to coarse, rod-like/blocky structures with increasing boron content. While both coatings achieved comparable microhardness and reduced friction coefficients compared to the substrate, the gradient design effectively alleviated interlayer stress concentration through compositional gradient optimization, reducing defects such as penetrating cracks, thereby achieving a coordinated optimization of microstructure and properties from the interfacial bonding zone to the surface layer.