Tuning strength–ductility synergy in LPBF 316L SS/TiB2 composites through nanoparticle dissolution and twinning activation

This work systematically investigates 316L stainless steel(316L SS) composites reinforced with 0.6 wt.% TiB 2 nanoparticles (D 50 = 800 nm) fabricated by laser powder bed fusion (LPBF) followed by post-heat treatment, aiming to achieve an optimized strength–ductility synergy. Laser energy density (ED) is identified as the key processing parameter because it directly governs the dissolution fraction of TiB 2 and consequently controls coherent interfacial phase formation and stacking-fault energy (SFE). An intermediate ED enabling partial dissolution of 0.12–0.2 wt.% TiB 2 is optimal, promoting the formation of ∼5 nm coherent M 3 B 2 interfacial layers and reducing the SFE to ≤ 50 mJ·m -2 , thereby enhancing interfacial bonding and activating deformation twinning. Under these conditions, the composite attains an ultimate tensile strength (UTS) of 1005 MPa and a total elongation (TE) of 28.5%, surpassing conventional and previously reported LPBF-processed 316L SS composites. In contrast, dissolution below 0.12 wt.% limits interfacial phase formation, whereas dissolution above 0.20 wt.% increases the SFE (> 50 mJ·m -2 ) and suppresses twinning. The subsequent solution treatment at 1050 °C for 30 min reduces yield strength but markedly improves work-hardening capacity and ductility (UTS = 876 MPa, TE = 52.5%) through twinning-dominated deformation in coarsened grains, accompanied by diminished hetero-deformation-induced (HDI) back-stress hardening that is characteristic of the as-built heterogeneous microstructure. Overall, this study establishes a dual-process strategy in which LPBF parameters and post-heat treatment are tuned to regulate TiB 2 dissolution, SFE, and grain size/heterogeneity, providing a mechanistic framework for designing high-performance metal matrix composites with controllable strength–ductility trade-offs.