Direct evidence of TiC nanoparticle-induced nucleation in laser powder bed fused AlSi10Mg

Grain refinement in AlSi10Mg fabricated by laser powder bed fusion was investigated via nano-TiC addition. Electron backscatter diffraction and scanning electron microscope analyses reveal that a 0.6 wt% nano-TiC addition reduces the average grain size by ∼71 %, promoting predominantly equiaxed morphologies while suppressing columnar growth. Transmission Kikuchi diffraction and energy dispersive X-ray spectroscopy analyses show that TiC nanoparticle clusters are commonly situated at grain centres, suggesting a potential cluster-mediated mechanism, whereas nucleation is linked to individual TiC particles that exhibit favourable orientation relationships with the Al matrix. Two plausible mechanisms—single-particle activation within clusters and cluster-mediated nucleation—likely operate concurrently, with particle pushing–engulfment dynamics explaining redistribution of TiC nanoparticles to interdendritic boundaries. These findings highlight the interplay of nanoparticle size, crystallography, and local solidification conditions in driving robust grain refinement under additive manufacturing.