The origin of the indentation size-effect was studied using convergent beam electron diffraction in a transmission electron microscope in order to map the crystal lattice rotations that occurred beneath low-load indentations made at loads of 5 and 15mN in copper. It was shown that the measured rotations were greater underneath the larger indentation. This was inconsistent with the predictions of strain gradient plasticity, although there appeared to be no other substantial differences in the deformation patterns. It was therefore suggested that the observed increase in hardness at the lower load was associated with the reduced probability of finding a suitable dislocation source in the loaded volume.

Deformation Underneath Low-Load Indentations in Copper. K.K.McLaughlin, W.J.Clegg: Journal of Physics D, 2008, 41[7], 074007 (5pp)