High-density nanocrystalline (n-) copper with the density more than 96 % of bulk copper is prepared by a gas-deposition method. The hardness of n-copper is more than four times higher than those of the polycrystalline copper. Beyond a certain applied stress, the steady-state creep rate showed a steep increase by a few orders. These characteristic mechanical properties are very similar to those observed for the almost fully dense n-gold. We surmise that coexistence of the high strength and the large plastic deformation at higher stresses is the common feature for fcc n-metals owing to the grain boundary regions with the much increased volume fraction. Since copper can easy be removed by chemical etching, it is a promising candidate for the housing material of micromachines with fine and complex shapes.
