nanotwinning

Nanotwinning is a deformation mechanism in crystalline materials in which a high density of nanoscale twin boundaries forms inside grains, creating a lamellar microstructure of coherent twin boundaries that mirror the lattice on opposite sides of each boundary. These nanoscale twins, or nanotwins, are typically separated by a few nanometers to a few tens of nanometers.

Nanotwins can arise during plastic deformation, rapid solidification, or specific processing routes such as severe plastic deformation and electrodeposition. They are especially well documented in face-centered cubic metals, including copper, nickel, and gold, where processing conditions favor the formation and stabilization of coherent twin boundaries. The density and spacing of nanotwins can be controlled through temperature, strain rate, and processing technique, enabling a tunable microstructure.

The coherent twin boundaries produced by nanotwinning are highly ordered, low-energy interfaces that interact strongly with dislocations. The resulting microstructure can significantly raise yield strength while preserving or even enhancing ductility, a combination often described as strength–ductility synergy. The mechanisms involve impeded dislocation motion, altered dislocation storage, and controlled plastic flow across twin boundaries. Because twin boundaries can be nearly as transparent to certain dislocations as conventional grain boundaries are obstructive, nanotwinned materials may also exhibit improved strain hardening and resistance to fatigue.

Characterization typically relies on transmission electron microscopy to resolve nanoscale twins, complemented by diffraction techniques to assess average twin spacing. Applications of nanotwinned metals include high-strength, high-conductivity copper and other alloys where a balance of strength and electrical or thermal performance is desirable.