Simultaneously increasing the strength and ductility of a Ni-Co-based superalloy via dual-heterostructure design

Abstract

Ni-Co-based superalloys are recognized as promising materials for the turbine discs of next-generation aero-engines, but the internal strength-ductility trade-off limits their applications. Here, we present a dual heterostructured Ni-Co-based superalloy characterized by harmonic grain heterostructure comprising fine grains and ultrafine grains, which is accompanied by bimodal-sized γ′ precipitates. The superalloy exhibits an outstanding strength-ductility synergy, with high yield strength (∼1.5 GPa) and ultimate tensile strength (∼1.8 GPa), concurrent with high uniform elongation (∼21 %), which is much higher than its solution and aging counterparts and superior to most superalloys. The excellent tensile properties primarily originate from its distinctive heterostructure and work hardening mechanism. The inhomogeneous plastic deformation leads to a high density of geometrically necessary dislocations pile-up near the hetero-zone boundaries, yielding so-called hetero-deformation-induced hardening. Besides, the bimodal-sized γ′ precipitates effectively impede dislocations slip to improve work hardening capacity. Additionally, stacking faults, Lomer-Cottrell locks and twins also contributed to the strain hardening. These findings suggest that the dual heterostructure design strategy is promising to improve the strength-ductility synergy in Ni-Co-based alloys.