A dislocation bow-out model was developed in order to explain the strength of ultra-fine grained materials having grain sizes of about 20 to 500nm. In the model, perfect dislocations were assumed to be nucleated at grain-boundary sources and bowed out between two pinning points on a boundary. Yielding was considered to occur when a dislocation takes a semi-circular shape under applied stress. Statistical consideration was introduced to evaluate the most probable pinning-point distance as a function of grain size. Comparison with experimental results was made for face-centered cubic ultra-fine grained metals. It was found that yield stress as well as thermal activation parameters could be explained reasonably by the present theoretical model.

Dislocation Bow-Out Model for Yield Stress of Ultra-Fine Grained Materials. M.Kato, T.Fujii, S.Onaka: Materials Transactions, 2008, 49[6], 1278-83