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.