Metals That Heal Themselves

A nuclear reactor is a grueling place for the metals there—all the wear-and-tear caused by neutron activities inside the reactor can make them swell and become brittle over time.
Researchers at Los Alamos National Laboratory in New Mexico have shown that by altering the microstructure of metals, metallurgists may be able to make reactor parts that are self healing.
Blas P. Uberuaga, Xian-Ming Bai and colleagues conducted computer simulations of the long-term impact of neutron emissions on copper — not because much copper is used in nuclear plants, but because it is a relatively well-modeled metal. Their findings are published in Science.
When a neutron hits metal, it displaces atoms within the crystal lattice. In a metal with a largely uniform structure, these atoms move to the surface, eventually causing the metal to swell, and the vacancies they leave behind can lead to voids that further weaken the material.
But it is possible to fabricate metals that have a nonuniform structure, with very small crystal grains, or regions of different phase or orientation. When atoms are displaced in this nanocrystalline material, rather than traveling to the surface they migrate to the boundaries between the grains. In their simulations, the researchers found that these atoms can then travel back away from the boundary and, if they find a vacancy, fill it, in effect healing the defect.