Influence of TiC Particle Modification on the Microstructure and Mechanical Properties of LPBF-Fabricated 316L Stainless Steel and Copper Multi-Material Structures

Laser powder bed fusion (LPBF) enables the fabrication of complex metallic components, yet processing dissimilar systems such as copper and 316L stainless steel presents severe challenges due to mismatched physical and thermal properties. This study provides new insights into the role of atomized spheroidal TiC reinforcement in controlling densification, microstructure, and localized deformation mechanisms in LPBF-fabricated Cu- and 316L-based composites and their multi-material joints. Spheroidal TiC particles were introduced at 2 and 4 wt.% into copper and 316L powders via V-type rotary mixing. The microstructural and mechanical response was evaluated through quantitative porosity analysis, Vickers microhardness testing, uniaxial tensile testing, and digital image correlation (DIC) strain mapping. In the copper matrix, adding 2% wt. TiC effectively reduced porosity from 0.83% to 0.44%, yielding an ultimate tensile strength of Rm ≈ 190 MPa and total elongation of 26% compared to 110 MPa and lower ductility for unreinforced LPBF copper. Increasing the TiC content to 4% wt. enhanced strength to Rm ≈ 250 MPa (Rp0.2 ≈ 180 MPa), although elongation decreased to 16%. In the 316L matrix, TiC addition progressively increased mean microhardness from 175.00 to over 322.25 HV0.1; however, 4% wt. TiC induced severe lack-of-fusion defect formation, resulting in a critical porosity of 10.59% and reduced ductility (12%). A DIC strain field analysis demonstrated that 2% wt. TiC promotes uniform strain distribution prior to necking, delaying localized failure. For Cu–316L multi-material joints, reinforcing the copper zone with 2% wt. TiC improved joint integrity, increasing tensile strength from ~110 MPa to ~190 MPa with a maximum elongation of 26%. These findings explicitly demonstrate that tailoring reinforcement concentration is vital to optimizing densification and mitigating strain localization in LPBF multi-material structures.