Strengthening Ni alloys with nanoscale interfaces of negative excess energy.

The strength of nanograined and nanotwinned metals is limited by the inherent instability of grain or twin boundaries below a length scale of typically about 10 nanometers. From experimental and density functional theory calculations, we found that the coherent interfaces between face-centered-cubic and hexagonal-close-packing lattices with a negative excess energy were more stable than twin boundaries in supersaturated Ni(Mo) solution. The negative excess-energy interface can be produced at extremely high density in Ni(Mo) solution with average spacing as small as about 1 nanometer, which inhibits plastic deformation and elevates the strength close to the theoretical value of the alloys. The measured Young's modulus of the Ni(Mo) alloys increases obviously with the interface density, reaching 254.5 gigapascals, well above that of the same compositional metallic glass and intermetallic compound (Ni3Mo).