Superior mechanical properties of additively manufactured FV520B matrix composites by microstructure tailoring

The additively manufactured martensitic stainless steel (SS) parts often manifest the strength-ductility trade-off dilemma, which severely limits their practicality. In this study, the TiC-reinforced FV520B metal matrix composites (MMCs) were deposited via laser powder bed fusion (LPBF), and the as-built MMCs exhibited a superior strength-ductility synergy (ultimate tensile strength of 1,389 +/- 29 MPa, and fracture elongation of 30.1 +/- 0.6 %) when compared to their matrix alloy. This strength-ductility synergy can be attributed to a high-density of welldispersed TiC nanoparticles, in-situ grain boundary engineering induced by TiC particles, fully austenite structure, and progressive transformation-induced plasticity effect. Furthermore, the microstructure, and mechanical properties of the MMCs annealed at 400-700 degrees C were compared. As the annealing temperature increases, the matrix progressively transforms from a fully austenite structure to a fully martensite structure, enabling substantial enhancements in tensile strength and work hardening capabilities. Notably, a high number density of the Cu-rich precipitates (CRPs) can be observed in the high-temperature annealed specimen, which can yield considerable strengthening through the Orowan looping mechanism. This work paves a pathway to fabricate structural materials with unique microstructures and excellent mechanical properties for practical engineering applications.