 Chandross & Argibay modeled grain boundary sliding as viscous flow and related the yield strength of the material in this regime to material properties as 
where formula_10 is the enthalpy of fusion, formula_11 is the atomic volume in the amorphous phase, formula_12 is the melting temperature, and formula_13 is the volume fraction of material in the grains vs the grain boundaries, given by formula_14, where formula_15 is the grain boundary thickness and typically on the order of 1 nm.The maximum strength of a metal is given by the intersection of this line with the Hall-Petch relationship, which typically occurs around a grain size of formula_8 = 10 nm for BCC and FCC metals .Due to the large amount of interfacial energy associated with a large volume fraction of grain boundaries, nanocrystalline metals are thermally unstable.