Hydrogen-Stabilized Dual-Phase Architecture Enables Exceptional Ductility in Refractory Molybdenum Nanowires

Enhancing the ductility of refractory body-centered cubic (BCC) metals at the nanoscale remains a formidable challenge due to the intrinsically limited dislocation mobility, which often leads to premature brittle fracture. Here, we report the construction of a face-centered cubic (FCC)/BCC dual-phase structure in Mo nanowires (NWs) via non-equilibrium electron-stream excitation (electric current or electron-beam irradiation). Atomic-scale characterizations and first-principles calculations suggest that interstitial hydrogen can stabilize the FCC phase at the NW surface. Unexpectedly, the dual-phase NW shows a high uniform ductility of ~41.4% along the [011] direction, representing a nearly 300% enhancement compared to the single-phase BCC NWs. This extraordinary mechanical behavior originates from a two-fold deformation mechanism mediated by hydrogen: (1) During the initial plastic deformation, a discrete two-step FCC-to-BCC transformation proceeds via fractional dislocation slip, which effectively relieves local stress concentrations and thus inhibits surface crack initiation; (2) As deformation continues, we find that H can promote dislocation nucleation based on the analysis of surface energy and unstable stacking fault energy, thereby sustaining continuous plastic flow and delaying failure. The proposed strategy offers a pathway to overcome the inherent brittleness of nanosized Mo metals, opening up new opportunities for their application in advanced nano-electromechanical systems.