Strength of nanoscale metallic multilayers

The relationship between microstructure, dislocation motion and mechanical response of metallic multilayered nanomaterials is investigated. Several competing theories for the dependence of hardness on layer thickness, namely Confined Layer Slip (CLS) and Hall-Petch (H-P) theories are discussed. Analysis of homophase and heterophase experimental data suggests that Hall-Petch with modified coefficients provides a good fit down to layer thicknesses of about 5 nm, below which experimental data starts to deviate. We suggest that at this layer thickness, dislocations accumulate in the interface, and assuming there is a constant dislocation density in each interface, the strength varies as h ^−1/2.