Multiscale evolution of TiC particles in GH3536-based composites fabricated via laser powder bed fusion: coarsening mechanisms and hierarchical distribution

The laser powder bed fusion (LPBF) of metal matrix composites (MMCs) involves distinctive rapid melting and nonequilibrium solidification dynamics. Elucidating the intricate evolution mechanisms of particles is critical for fabricating MMCs with superior strength-ductility synergy. In this study, both GH3536 Ni-based alloy and 5 wt% TiC-reinforced GH3536 composites (GH3536-5TiC) were fabricated via LPBF. The influence of volumetric laser energy density on the microstructure, mechanical properties, and multiscale evolution of TiC particles was systematically investigated. The experimental results revealed that a positive correlation existed between the energy density and both the TiC particle loss rate and average particle size, which was attributed to the coarsening and spattering behaviour of TiC particles, as demonstrated through multiscale evolution simulations. A dimensionless quantities framework based on kinetic calculations of the melt pool was established to determine the effect of energy density on TiC particle evolution. The growth mechanism of nanoscale TiC particles (<100 nm) is primarily governed by chemical transport, while microscale TiC particles (3–7 µm) mainly undergo impingement-driven coarsening. Low energy density was found to reduce the impingement-driven coarsening. In addition, this study demonstrated the hierarchical distribution of TiC particles after multiscale evolution. Compared to GH3536, the GH3536-5TiC fabricated under low energy density conditions demonstrated significantly enhanced tensile performance. At 1 173 K, its ultimate tensile strength and elongation values were found to be 304 MPa and 42%, respectively. Overall, this work provides a theoretical guideline for the performance optimisation of additively manufactured advanced composites via controlling the evolution of reinforcements.