Modelling nanoscale grain size strengthening or weakening according to grain boundary thickness

Abstract

The relationship of yield stress and grain size at nanoscale is modelled in this letter. The deformation behaviour of materials is divided into two regions: the grain rotation at the boundaries and deformation in the inner ordered region. It is found that the yield stress reaches its maximum when the grain size, d, is three times of the grain boundary thickness, t, corresponding to a 70% volume ratio of grain boundaries. When d>3t, the interface area increases with grain size reduction, leading to the yield stress increment. When d<3t, the interface area decreases with grain size reduction, leading to the yield stress decrement. The hardness has similar trend. The proposed model agrees well with the documented data in Cu, Fe, Pd and NiP alloys.