Effect of TiC content on precipitation microstructure and properties of multi-layer laser-cladded Ni-based composite coatings

This study systematically investigates the synergistic effect of TiC content (0–30 wt.%) and the preheating and tempering effects inherent in multilayer cladding on the microstructure, precipitate distribution, and mechanical properties of Ni60-based composite coatings. Coatings were fabricated on 45 steel and characterized by Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), microhardness and wear tests. The results reveal that preheating and tempering during multilayer cladding create a cooling-rate gradient along the coating height, leading to a stepwise evolution of precipitates from γ-Ni/[Fe,Ni] dendrites at the bottom, to CrB-type borides in the middle, and fine Cr-rich carbides at the top. Owing to their lower density than the Ni-based melt, TiC particles migrate upward under buoyancy, resulting in bottom-to-top enrichment and coarsening. TiC addition exhibits a non-monotonic effect on the microstructure and wear performance: an appropriate TiC content promotes heterogeneous nucleation, grain refinement, and dual-scale strengthening, whereas excessive addition causes TiC to become the dominant phase, leading to particle coarsening, spalling, and oxidative degradation. Although microhardness increases with TiC content, wear resistance does not follow the same trend. The coating with 20 wt.% TiC achieves the best overall performance, demonstrating that controlled TiC addition is critical for tailoring gradient precipitate distribution and improving wear resistance.