The well-known indentation size effect (ISE) is reviewed with special emphasis on
the effect of grain size in the polycrystalline matrix. It is demonstrated that there
is a close connection between the Hall-Petch relationship and the characteristics
of the ISE phenomenon such that the ISE phenomenon may disappear in an ultrafine-grained
(UFG) matrix. This finding is significant in any attempts to interpret nanoindentation
measurements performed on UFG materials.
