Modelling the strongest grain size in nanocrystalline FCC metals

A physical model is proposed to predict the critical grain size at which nanocrystalline FCC metals reach a maximum steady state flow stress. The model considers that nanocrystalline metals are composed of two phases. One is the grain boundary phase and the other is the grain interior phase. The grain boundary phase has specific deformation mechanism different to the grain interior phase. The critical grain size with the maximum steady state flow stress is predicted to decrease with deformation temperature and to increase with strain rate. Both normal and abnormal Hall–Petch relations can be described simultaneously by the model.