Acoustic emission in micropillar deformation experiments

Bulk materials generally deform homogeneously. However, if their size is considerably decreased the deformation becomes inhomogeneous and unpredictable. Consequently, traditional methods of metal forming become unusable in this size regime (that is, if the specimen size is around few µm at least in one direction). New probabilistic methods are, therefore, required that take into account the details of random local plastic events. To this end, it is necessary to provide an in-depth experimental investigation of these elementary deformation processes. In my poster, I would like to demonstrate some experimental results, which we achieved by the combination of two experimental methods: (i) nanoindentation testing used to determine the stress-strain characteristics of micrometer size samples, and (ii) acoustic emission measurement which is able to monitor plastic activities in bulk materials. The required micropillars were formed using a focused ion beam from Zn single crystals. The in situ nanoindentation experiment was carried out in a scanning electron microscope while a piezoelectric detector attached to the bottom of the sample recorded the acoustic signals. Our simultaneous measurements show a real correlation between the dislocation avalanches associated with the measured stress drops and the detected acoustic signals. This indicates that the sudden collective motion of dislocations induce the deformation, indeed. We could successfully apply this method to investigate the dependence of the deformation on the size and crystal orientation. Thus we hope that this type of measurement will further deepen our knowledge on the statistical properties of these elementary deformation mechanisms.