Enhanced cryogenic strength of directed energy deposited 316L through TiC reinforcement and its deformation mechanisms

초록

Achieving cryogenic strengthening in additively manufactured 316 L stainless steel while retaining ductile deformation remains challenging, particularly when ceramic reinforcements are introduced. In this study, a 316 L/TiC composite was fabricated by incorporating 2 wt% TiC nanoparticles via directed energy deposition (DED), and the correlation between microstructure and mechanical properties was systematically investigated at room temperature and 77 K. The addition of TiC refined the grain size and increased the dislocation density from 2.95 × 1015 to 3.71 × 1015 m−2, while uniformly dispersed TiC particles provided additional obstacle strengthening. As a result, the 316 L/TiC composite exhibited higher strength than 316 L at both temperatures (RT: 556/761 MPa; 77 K: 908/1418 MPa). Notably, a higher fraction of γ-austenite was retained during cryogenic deformation in the TiC-reinforced sample, suggesting relatively enhanced phase stability. This behavior is attributed to the increased dislocation density and strong ceramic particle–dislocation interactions, which suppress deformation-induced martensitic transformation and deformation twinning, thereby promoting slip-dominated plastic deformation. Despite the suppression of transformation mechanisms, an increased strain hardening rate and ductile fracture characteristics were maintained. These results show that nanoparticle-induced changes in deformation behavior and the transition to slip-dominated deformation play an important role in mechanical behavior. They also provide a useful strategy for designing metal–ceramic composites. © 2026 Elsevier B.V.

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