Particle-size effect and strengthening mechanisms in laser shock-molten pool-assisted cored wire arc directed energy deposition of Inconel 625 composites

In cored wire-arc directed energy deposition (DED), interactions between reinforcement particles and the molten pool critically govern the microstructural integrity and performance of metal-matrix composites. This study incorporates laser shock processing into TiC-reinforced Inconel 625 wire-arc DED to regulate molten-pool behaviour and enhance particle dispersion. TiC reinforcements with three characteristic size ranges – micron (15-45 μm), submicron (1–5 μm), and nano (300–500 nm) – are systematically investigated to elucidate their effects in molten-pool dynamics, solidification behaviour, defect evolution, and mechanical and tribological performance. Multiscale characterisation combined with mechanical and wear testing demonstrates that TiC particle size strongly influences the temperature gradient and solidification rate, enabling an laser shock-assisted columnar-to-equiaxed grain transition. Submicron-scale TiC exhibits the most effective heterogeneous nucleation and interfacial stability, resulting in uniform grain refinement, dislocation network formation, residual-stress homogenisation, and suppression of void-assisted cracking. In contrast, micron-scale TiC provides limited nucleation capability, whereas nanoscale TiC tends to agglomerate, destabilise the molten pool, and promote defect accumulation. Consequently, submicron-scale TiC achieves the optimal strength-ductility balance and superior wear resistance through synergistic Hall-Petch strengthening, Orowan pinning, and tribo-oxidative film formation. This work establishes a mechanistic framework linking reinforcement size, solidification behaviour, defect architecture, and multiscale strengthening in laser shock-assisted wire-arc DED.Highlights A stable laser shock-assisted cored-wire-arc DED strategy is developed to enhance build quality.The influence of particle size on forming behaviour, microstructure, and mechanical properties is revealed.Submicron-scale TiC improves microstructural integrity through heterogeneous nucleation.Size-dependent particle strengthening mechanisms are experimentally confirmed.