Effects of nano-CeO₂ particles on the microstructural evolution and tribological performance of laser-deposited Ni45 coatings

This study presents a systematic investigation into the role of nano-CeO₂ particles in enhancing the tribological performance of LDED Ni45 coatings on martensitic stainless-steel substrates. An advanced powder metallurgy, precision LDED processing, and multi-scale characterization were used to decode the relationship between CeO₂ concentration, microstructure evolution, and wear performance. Four distinct CeO₂ concentrations (0, 0.5, 1, and 2 wt%) were incorporated into Ni45 powders and then deposited on substrates. The critical CeO₂ concentration threshold was identified at 0.5 wt%, achieving synergistic performance enhancement through three mechanisms: 44 % grain refinement via CeO₂-induced heterogeneous nucleation; Significant increase in hard phase (Cr 23C 6/Cr 5B 3) content with optimized spatial distribution and formation of Ce-stabilized nanocrystalline domains through pinning. These microstructural modifications yielded exceptional tribological performance 85.9 % reduction in specific wear rate and 44.1 % lower steady-state friction coefficient compared to uncoated substrates. However, higher CeO₂ concentrations induced performance degradation through nanoparticle agglomeration, accelerated oxygen diffusion along Ce-segregated boundaries, and dendritic growth promoting crack propagation. It can be concluded that below 0.5 wt%, CeO₂ enhances load-bearing networks through solid solution strengthening, Hall-Petch strengthening from refined grains, Orowan dislocation pinning by Ce-rich nanoclusters and precipitation hardening of reinforced phases dominated by carbides and borides; beyond this threshold, agglomeration-induced stress concentrations dominate. This work provides fundamental insights for designing wear-resistant coatings in high-stress industrial applications.