Enhanced mechanical properties of LPBF-fabricated CoCrNi/TiN composites via in-situ nanoparticle reinforcement

The incorporation of ceramic nanoparticles into medium-entropy alloys offers a promising route to enhance mechanical performance through microstructural engineering. In this study, CoCrNi composites reinforced with 1–2 wt% TiN nanoparticles were fabricated via laser powder bed fusion (LPBF), achieving a remarkable synergy of strength and ductility. The addition of 1 wt% TiN increased the yield strength and ultimate tensile strength from 694.5 MPa to 955 MPa–806 MPa and 1084 MPa, respectively, while the fracture elongation remained comparable (33 % → 33.5 %). During LPBF, TiN nanoparticles decomposed in situ, forming semi-coherent TiN and TiO₂ precipitates. By exerting a pinning effect and raising the energy barriers for twin propagation, these semi-coherent particles suppress twin formation and growth. Strengthening mechanisms were quantitatively assessed, revealing a dominant contribution from precipitation hardening (136.9 MPa and 205.1 MPa for 1 wt% and 2 wt% TiN, respectively), supplemented by dislocation, grain boundary, and strain hardening effects. This work demonstrates the potential of LPBF-processed CoCrNi-TiN composites for high-performance applications and provides a framework for tailoring strength-ductility balance via nanoparticle-induced microstructural control.