Approaching Theoretical Strength in a Ductile Nanograined Fe–Ni Alloy via the Phase Engineering Strategy

Approaching the theoretical strength of ductile metals is an interesting challenge for enabling new generations technologies. Dual-phase alloys are known for their exceptional balance between strength and ductility. In this study, phase transformations were strategically induced in the BCC single-phase nanograined (NG) Fe–Ni alloy synthesized via inert gas condensation (IGC). Aging at 300 °C resulted in the formation of a BCC–FCC (body-center cubic and face-center cubic) dual-phase structure. Microcompression experiments revealed that the NG Fe–Ni alloy annealed for 10 h achieved an ultrahigh yield strength of 4800 MPa, approaching the theoretical strength, while maintaining considerable ductility of 24%. Phase transformation promoted dislocation exhaustion during prolonged annealing, which contributes to the ultrahigh strength of the Fe–Ni alloy. Furthermore, the proportion of the FCC phase increased further contributes to ductility retention. These findings highlight the potential of phase engineering in NG metallic materials, offering a promising method for designing a class of devices potentially suitable for high-stress applications.