TiC nanoparticles tune phase stability and deformation mechanisms in directed energy deposition processed Fe60Co15Ni15Cr10 medium-entropy alloy composites

Abstract

Additive manufacturing (AM) of particle-reinforced metal matrix composites (MMCs) offers opportunities not only for mechanical strengthening but also for tailoring matrix phase stability and deformation behavior. In this study, TiC (2 wt%) nanoparticles were incorporated into Fe60Co15Ni15Cr10 (at%) medium-entropy alloy (MEA) using directed energy deposition (DED) process. Despite the severe thermal conditions of the DED process, a substantial fraction of TiC remained, while partial decomposition released C and Ti elements into the matrix. This chemical modification stabilized the gamma-austenite matrix phase and suppressed deformation-induced martensitic transformation (DIMT), which is typically active in the Fe60Co15Ni15Cr10 MEA. Instead, the composite exhibited a transition toward slip-dominated deformation. Microstructural observation revealed that dispersed and semi-coherent TiC particles, together with solute partitioning from decomposed nanoparticles, altered grain boundary morphology and promoted distributed plastic flow. In-situ neutron diffraction accompanied with tensile test confirmed enhanced dislocation activity in the early stage of deformation, supporting the deformation mechanism shift from DIMT-assisted hardening to dislocation-mediated slip. These results highlight the critical role of nanoparticle-induced phase stability variation in governing deformation mechanisms, offering new insights into designing AM-processed MMCs beyond conventional strength-oriented strategies.