Berlin 2015 – wissenschaftliches Programm
MM 28.15: Poster
Dienstag, 17. März 2015, 18:30–20:30, Poster E
Plasticity at the low end of the nanoscale - a crossover to glass-like behavior? — •Christian Braun, Manuel Grewer, and Rainer Birringer — Universität des Saarlandes, FR 7.2 Experimentalphysik, Campus D2.2, 66123 Saarbrücken
Polycrystalline metals at the low end of the nanoscale with grain sizes of 10 nm or less are characterized by a grain boundary volume fraction of at least 30%. Grain boundary deformation modes similar to shear transformations (STs) in bulk metallic glasses (BMGs) may therefore play a non-negligible role in the mechanical behavior of nanocrystalline (nc) metals. In fact, a couple of similarities between this two material classes have been observed, e.g. comparable values for the shear activation volume, activation energy or Mohr-Coulomb friction coefficient. However, in BMGs increasing load involves percolation of STs followed by shear band formation manifesting stick-slip behavior that eventually leads to catastrophic failure. In contrast, for nc Pd90Au10 we observe absence of stick-slip behavior implying that shear banding is missing. In fact, the operation of STs at/along grain boundaries in conjunction with the network constraints of the nanoscale microstructure avoids pronounced shear band propagation. We present results of mechanical testing of nc Pd90Au10 samples synthesized by inert gas condensation and deformed in shear compression geometry under different loading conditions. These results are analyzed in terms of activation parameters and pressure or normal-stress dependence of plasticity. Furthermore, the interplay and the succession of active deformation mechanisms are investigated using in situ X-ray diffraction.