Direct Observation of Grain-Boundary-Migration-Assisted Radiation Damage Healing in Ultrafine Grained Gold under Mechanical Stress.

Nanostructured metals are a promising class of radiation-tolerant materials. A large volume fraction of grain boundaries (GBs) can provide plenty of sinks for radiation damage, and understanding the underlying healing mechanisms is key to developing more effective radiation tolerant materials. Here, we observe radiation damage absorption by stress-assisted GB migration in ultrafine-grained Au thin films using a quantitative in situ transmission electron microscopy nanomechanical testing technique. We show that the GB migration rate is significantly higher in the unirradiated specimens. This behavior is attributed to the presence of smaller grains in the unirradiated specimens that are nearly absent in the irradiated specimens. Our experimental results also suggest that the GB mobility is decreased as a result of irradiation. This work implies that the deleterious effects of irradiation can be reduced by an evolving network of migrating GBs under stress.

A nanodispersion-in-nanograins strategy for ultra-strong, ductile and stable metal nanocomposites.

Nanograined metals have the merit of high strength, but usually suffer from low work hardening capacity and poor thermal stability, causing premature failure and limiting their practical utilities. Here we report a "nanodispersion-in-nanograins" strategy to simultaneously strengthen and stabilize nanocrystalline metals such as copper and nickel. Our strategy relies on a uniform dispersion of extremely fine sized carbon nanoparticles (2.6 ± 1.2 nm) inside nanograins. The intragranular dispersion of nanoparticles not only elevates the strength of already-strong nanograins by 35%, but also activates multiple hardening mechanisms via dislocation-nanoparticle interactions, leading to improved work hardening and large tensile ductility. In addition, these finely dispersed nanoparticles result in substantially enhanced thermal stability and electrical conductivity in metal nanocomposites. Our results demonstrate the concurrent improvement of several mutually exclusive properties in metals including strength-ductility, strength-thermal stability, and strength-electrical conductivity, and thus represent a promising route to engineering high-performance nanostructured materials.