When a metal is forged, stamped, or otherwise strained, it hardens. The change in mechanical properties arises from dislocations in the crystal lattice that enable adjacent planes of atoms to slide past each other. As the metal is worked, the dislocations accommodate the strain; but in doing so, they become entangled, pile up at existing grain boundaries, and produce countless new ones that impede the dislocations’ movement and make the metal harder to deform.
For decades, materials scientists have known that nanostructuring a metal—deforming it plastically until the grains shrink to submicron dimensions—can increase its yield strength by as much as an order of magnitude. But many of the newly formed interfaces are unstable: In the harsh environment of a hot jet engine, say, or an irradiating nuclear reactor, grains can grow larger or become decorated by voids due to the agglomeration of lattice vacancies. In either case, the metal...
