By using in situ nano-indentation techniques in a transmission electron microscope, the indentation-induced plasticity of ultrafine-grained thin films was studied; together with conventional quantitative nano-indentation. Extensive grain boundary motion was observed in pure Al, whereas Mg solutes effectively pinned the high-angle grain boundaries in Al–Mg films. The mechanism proposed for this pinning was a change in the atomic structure of the boundaries; perhaps aided by solute drag on extrinsic grain boundary dislocations. The mobility of the low-angle boundaries was not affected by the presence of Mg. Based upon direct observations of incipient plasticity in these materials, it was concluded that solute drag accounted for the absence of discrete strain bursts during the indentation of Al–Mg.

Effects of Solute Mg on Grain Boundary and Dislocation Dynamics during Nanoindentation of Al–Mg Thin Films. W.A.Soer, J.T.M.De Hosson, A.M.Minor, J.W.Morris, E.A.Stach: Acta Materialia, 2004, 52[20], 5783-90