Synergistic enhancement of high temperature strength and ductility with a novel γ/ε dual-phase hetero-nanostructure in NiCoCr-based alloys

In most γ"-strengthened superalloys, the γ"→δ stabilization is generally considered as an unfavorable transformation process due to the incapability of δ phase on conferring high-temperature strengthening. While recent studies in multi-component alloys indicate that another stabilized γ" phase (ε phase with D019 structure) has been found and proven to be beneficial to mechanical properties. This work shows that the precipitation of ε phase could be tailored in such a way, that it is accompanied by the formation of nano-twins in low stacking fault energy NiCoCr-based multi-component alloys, establishing a unique matrix/(nano-twin/ε/nano-twin)/matrix double-stacked-sandwich heterogeneous nanostructure. This novel ε-plate/nano-twin structure has been found to provide satisfying high temperature strength-ductility synergy and structural stability after aging, thereby leading to a yield-strength enhancement of ∼120% at 25 °C and ∼98% at 700 °C, respectively, while still maintaining sound ductilities. This unique self-organized, heterogeneous, lamellar nanostructure opens up new avenues for further development of hierarchically-nanostructured, high-temperature structural materials.