Strengthening mechanisms in nickel-based composites fabricated by multiscale-enhanced in-situ synthesis by laser powder bed fusion

• A multiscale TiC reinforcement strategy was developed for IN738LC, enabling in-situ formation of nano-TiC during L-PBF. • In-situ multiscale TiC reinforcement offers better strength–ductility synergy than direct nanoparticle mixing. Nickel-based superalloys are widely used in aerospace due to their excellent high-temperature mechanical properties. To optimize these properties and minimize particle damage during powder preparation, this study proposes a multiscale titanium carbide (TiC) reinforcement strategy for IN738LC superalloy using Laser Powder Bed Fusion (L-PBF). A composite feedstock was prepared by mixing coarse (10–20 μm) and fine (0.5–4 μm) TiC particles with IN738LC powder. During L-PBF, in situ reactions formed nano-TiC phases, promoting significant grain refinement. A full-factorial experimental design evaluated the effects of laser power, scanning speed, and hatch spacing on porosity, microhardness, and tensile properties, identifying optimal parameters of 150 W, 500 mm/s, and 0.09 mm, respectively. Multiscale TiC reinforcement led to improved strength and hardness, with ductility slightly reduced but still superior to conventional mixing routes. Microstructural analysis revealed enhanced grain refinement (from 59.1 μm to 29.8 μm), reduced residual stress, and suppressed oxides and cracks. Compared to single-scale nano-TiC approaches, the multiscale strategy achieved better microstructural homogeneity and mechanical performance. This study demonstrates the feasibility and advantages of multiscale TiC reinforcement, providing a promising pathway for advancing the additive manufacturing of high-performance nickel-based superalloys.