Melt pool evolution, microstructure and fracture toughness analysis of nickel-based composite coating deposited by laser-based directed energy deposition on 316L stainless steel

This study systematically analyzed the effects of varying SiC content on the melt pool dynamics, bonding strength, microstructure, and mechanical properties of nickel-based composite coatings produced by laser-based directed energy deposition (DED-LB) on 316 L stainless steel substrates. The results showed that increased SiC content significantly altered the melt pool dimensions, with higher SiC content enhancing the thermal conductivity of the composite powder, leading to melt pool expansion and increased fluidity. Surface roughness initially decreased and then increased with overlap ratio, with the 50 % overlap producing the lowest surface roughness and highest bonding strength. Microstructural observations revealed that higher SiC content led to significant grain refinement and promoted uniform distribution of Cr-enriched phases and Si, though excessive SiC content caused carbon aggregation, increasing brittleness in localized regions. Higher SiC content also promoted the formation of carbides and silicides while suppressing the precipitation of existing carbides. Additionally, SiC encouraged the formation of HAGBs. As SiC content increased, nano-mechanical properties, including nano-hardness and elastic modulus, were significantly enhanced, while fracture toughness gradually decreased, indicating increased brittleness.