Balancing strength and ductility in MP159 superalloy (Co–Ni–Cr–Fe–Mo–Ti–Al–Nb) through severe plastic deformation and multistage heat treatments

초록

This study investigated the enhancement of room-temperature mechanical properties in the Co-Ni-Cr-Fe-Mo-Ti-Nb-Al MP159 superalloy through severe plastic deformation via high-ratio differential speed rolling (HRDSR), followed by controlled annealing and aging treatments. Partial recrystallization during annealing produced a microstructure comprising recrystallized and unrecrystallized grains, enabling a favorable balance between strength and ductility. Optimal annealing at 1123 K for 48 h produced a partially recrystallized microstructure, consisting of fine recrystallized grains (∼2.2 μm) embedded in unrecrystallized regions. This microstructural configuration yielded a high yield strength of 0.83 GPa and a uniform elongation of 18.3 %. Subsequent aging promoted the formation of nanoscale L1<inf>2</inf>-type γ′ precipitates, further increasing the yield strength to 1.1 GPa while maintaining good uniform ductility (∼12 %). The mechanical response was analyzed considering grain refinement, dislocation density, recrystallization behavior, and precipitation strengthening. This integrated thermo-mechanical approach provides a practical and effective means of enhancing the strength–ductility synergy in MP159 superalloys for advanced structural applications. © 2025 Elsevier B.V.

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