Figure High-density coherent interfaces between face-centered-cubic and hexagonal-close-packing lattices are produced in supersaturated Ni(Mo) solution nanograins with a negative excess energy (A and B); these interfaces effectively inhibit plastic deformation and simultaneously enhance both strength and elastic modulus (C and D), pumping up yield strength close to the extreme (E).

Supported by the National Natural Science Foundation of China (Grant No. 52441407), the research teams led by Professors Ke Lu and Xiuyan Li from Liaoning Academy of Materials in collaboration with the Institute of Metal Research of Chinese Academy of Sciences, have discovered that the nanoscale interfaces of negative-excess-energy are highly stable in a Ni(Mo) supersaturated solution and elevate the material’s strength close to the theoretical limit and Young’s modulus well above that of the same-compositional metallic glass and intermetallic compound (Ni₃Mo). This research, titled “Strengthening Ni alloys with nanoscale interfaces of negative-excess-energy”, was published in Science on November 6, 2025 (https://www.science.org/doi/10.1126/science.aea4299).

Strengthening metals has been a longstanding endeavor in materials research for centuries. Grain refinement is an effective way to strengthen metals and alloys following the well-known Hall-Petch relation without changing their chemical compositions, as grain boundaries provide obstacles to resist dislocation slip. Remarkable hardening from nanoscale twin boundaries with very low excess energies has been observed in a number of metals and alloys, semiconductors, as well as ceramics in the last few years. However, both hardening effects may fade away due to thermodynamic instability when the nanostructures are below a threshold size, typically around 10-15 nm. Further strengthening of metals therefore calls for a new strategy to stabilize these hardeners at even higher densities.

Extremely-dense planar faults with an average spacing as small as ~1 nm were produced in a supersaturated Ni(Mo) solid solution by using pulse-current electrodeposition and a subsequent annealing process. The Ni(Mo) nanograins were characterized by densely mixed face-centered-cubic and hexagonal-close-packing lattices. Density functional theory calculations revealed that the coherent interfaces with a negative-excess-energy, ranging from -8.7 to -19.5 mJ/m², were more stable than coherent twin boundaries, which were believed to be the most stable interface in face-centered-cubic metals. These extremely dense negative-excess-energy interfaces effectively suppress dislocation motion and interface activities in plastic deformation, pushing the strength (5.08 GPa) of the metals close to its theoretical value. The obtained strength exceeds the highest strength of other metallic alloys in bulk forms, including steels and refractory alloys reported in the literature and is on par with strength of many oxides and nitrides. The measured Young’s modulus of the Ni(Mo) alloy increases significantly with the density of negative-excess-energy interfaces, reaching 254.5 GPa - well above that of the same-compositional metallic glass and intermetallic compound (Ni₃Mo). According to our DFT calculations, the nanoscale negative-excess-energy interface hardening effect, as observed in other Ni alloys including Ni-W, Ta, Nb, Mn and V, is expected to be applicable to different material systems.

The approach opens up many new possibilities, not only for materials development in a new dimension, but also for upgrading our understanding of the structure-property relationship in solids.