Study on the cryogenic treatment-induced precipitation of laves phase and strengthening mechanisms in Co25Fe25Mn20Ni25Ti5 high-entropy alloy

This study induced the precipitation of the Laves phase in a Co 25 Fe 25 Mn 20 Ni 25 Ti 5 (at.%) alloy through cryogenic treatment (CT) and combined cryogenic treatment with low-temperature tempering (CT + LT), leading to simultaneous enhancement of its mechanical properties. The as-cast microstructure consists of a single FCC phase, featuring Fe/Co-rich dendrites (DR) and Ni/Ti-rich inter-dendritic (ID) regions. After CT, fine Laves phase particles precipitated in the matrix, and the optimal strength–ductility balance (YS: 422.80 ± 6.58 MPa, EL: 28.54 ± 1.12 %) was achieved under the CT24LT condition. Significant orientation differences between grains induced intergranular rotation, which coordinated microscopic deformation and promoted Laves phase precipitation. The improved mechanical properties are attributed to Laves phase strengthening and dislocation strengthening. The hard Laves phase acts as non-deformable particles that strongly hinder dislocation motion, causing pronounced dislocation pile-ups and local stress concentration. Plastic flow proceeds via cross-slip, consistent with KAM evolution. Under CT24LT, the Laves phase exhibits a slightly larger size and more uniform distribution, which alleviates stress concentration and delays crack initiation. Moreover, multiple slip systems are activated, effectively suppressing premature failure. The increased average density of geometrically necessary dislocations (GNDs) enhances dislocation storage capacity and work-hardening behavior. In summary, the coordinated evolution of Laves phase characteristics and dislocation configurations optimizes the strength–ductility synergy, where second-phase and dislocation strengthening serve as the primary mechanisms. • Exploring the mechanism of CT to improve the properties of the CoFeMnNiTi HEA. • Cryogenic treatment induces the precipitation of Laves phase. • Laves phase and dislocation strengthening optimized its mechanical properties.