Yield stress of fine grained materials

A model is proposed for the yield stress of ultra-fine grained materials based upon Coble creep. Using Coble creep with a threshold stress for finer grains and conventional Hall-Fetch strengthening for larger grains, an analytical relation is derived for the yield stress as a function of grain size for a range from very large to very small. A grain size distribution is incorporated into the analysis to account for a distribution of grain sizes occurring in most specimens. This result is compared with experimental data from Cu and NiP and shown to be in good agreement. Acta Metallurgica Inc. Published by Elsevier Science Ltd.