Strength and plasticity of nanocrystalline metals with a bimodal grain structure

Using dislocation-kinetics equations, the structural factors are discussed that determine the strength and plastic properties of nanocrystalline metals with a bimodal grain structure containing not only nanograins but also a certain volume fraction of micron-sized grains. It is found that the plasticity (uniform strain) of nanocrystalline metals with a bimodal structure is significantly higher than that of a unimodal structure and the strength remains at the same high level. This improvement can be attained for a certain combination of factors, such as the relation between the grain sizes, the ratio of the volume fractions of nano- and micrograins in the bimodal structure, and the parameter determining the efficiency of grain boundaries as dislocation sources.