Gradient structured nanocrystalline–amorphous Fe-based composite coatings with superior strength and wear resistance

Abstract

Gradient nanocrystalline–amorphous nanostructures are considered to be an effective approach to achieve exceptional strength–plasticity synergy, with significantly improved wear performance. Here, gradient nanostructured Fe-based coatings were successfully fabricated by extremely high-speed-rate laser deposition and remelting. The microstructure evolution along the depth direction varies in a nanocrystalline, equiaxial dendrites, columnar dendrites gradient, respectively. Noticeably, amorphous grain boundaries and carbide nanoprecipitates could be identified within the topmost surface nanocrystalline layer owing to the extremely high cooling rate during remelting, which exhibits the highest hardness and wear resistance (microhardness of ∼1136 HV, and wear rate of 4.36 × 10⁻⁶ mm³/(m N)). The superior wear resistance is mainly attributed to the synergistic nanocrystalline–amorphous deformation and gradient refinement effects. Meanwhile, multi-scale carbides effectively impede dislocation motion and further improve strength and wear resistance at different depths. This gradient structure provides promising insights into the design of high-performance wear-resistant alloys.