The possibilities of using in situ transmission electron microscopy to clarify dislocation/grain-boundary interactions were considered. Attention was focused on the deformation characteristics of Al–Mg films, and in situ nano-indentation experiments were performed - in a transmission electron microscope - on ultrafine-grained Al and Al–Mg films having various Mg contents. The propagation of dislocations was observed to be markedly different in Al and Al-Mg films. That is, the presence of solute Mg resulted in solute drag; as revealed by jerky dislocation motion with a mean jump-distance that compared well with previous theoretical and experimental results. It was proposed that such solute drag accounted for the different load-controlled indentation responses of Al and Al-Mg alloys. Several yield excursions were observed during the initial indentation of pure Al, and were usually attributed to the collective motion of dislocations which were nucleated under the indenter. Displacement-controlled indentation did not result in a qualitative difference between Al and Al–Mg. This was attributed to the specific feedback characteristics, which provided a more sensitive detection of plastic instabilities and permitted natural load relaxation to occur. The in situ indentation measurements confirmed that grain boundary motion was an important deformation mechanism in ultrafine-grained Al when it was subjected to the highly inhomogeneous stress field produced by a Berkovich indenter. It was found that solute Mg pinned high-angle grainboundaries during this deformation. The mobility of low-angle boundaries was not affected by the presence of Mg.

In situ TEM Nanoindentation and Dislocation-Grain Boundary Interactions - a Tribute to David Brandon. J.T.M.De Hosson, W.A.Soer, A.M.Minor, Z.Shan, E.A.Stach, S.A.S.Asif, O.L.Warren: Journal of Materials Science, 2006, 41[23], 7704-19