The Role of Grain Size in the Mechanical Properties of Metals

It is now well established that the grain size is the fundamental microstructural feature of all polycrystalline materials. In practice, a very wide range of grain sizes will be needed in order to fully evaluate the effect of grain size on the mechanical properties of metals. For many years this was a significant limitation because it was not possible to use conventional thermomechanical processing to produce materials with submicrometer or nanometer grain sizes. Recently, this problem has been addressed by developing alternative processing techniques based on the application of severe plastic deformation. This overview demonstrates that, although the flow stress increases with decreasing grain size at low temperatures and decreases with decreasing grain size at high temperatures, this clear dichotomy in behavior may be adequately explained by using a single theoretical flow mechanism based on the occurrence of grain boundary sliding.