A SIMPLE, MIXTURES-BASED MODEL FOR THE GRAIN-SIZE DEPENDENCE OF STRENGTH IN NANOPHASE METALS

A model is presented for the strength of nanophase metals. The model assumes that polycrystalline metals consist of two phases: the ''bulk'' intragranular regions, and the ''grain boundaries.'' The boundary phase is treated as a glassy, but not highly rare-dependent material with a constant strength equal to that of the amorphous metal. The crystalline phase is assumed to follow a Hall-Fetch equation for the grain-size dependence of strength. Treating the material as a composite, with a rule of mixtures approach, predicts a change in the Hall-Fetch slope at small grain sizes, as has been observed. Grain size softening is predicted, but not until sizes below 5 nm. The model is compared to data in the literature.