Grain boundary plasticity in nanocrystalline alloys: Transition to glassy behavior?

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The goal of this project is to unravel the synergy and hierarchy of coexisting deformation modes in nanocrystalline (nc) PdAu-alloys at the low end of the nanoscale (< 10 nm). We put special emphasis on identifying and quantifying the evolution of shares of different elastic and plastic strain carrying deformation mechanisms. In the spirit of set theory, we have been able to identify that grain boundary mediated deformation mechanisms contribute in a dominant manner to overall strain in nc PdAu-alloys. We gathered ample evidence that shear tranformations (ST), the intrinsic flow event in disordered media, should be the active and dominant deformation mode in grain boundaries. In fact, we find that ST dominate the macroscopic deformation behavior. Based on a study of the stress dependence of the barrier height scaling in nc Pd90Au10, we could deduce a scaling relation for the stress strain-rate reponse of the material and conjecture that this viscoplastic material law should have universal character. The main trust of this proposal relies upon corroborating this conjecture. Since the observed stress dependence of barrier height scaling is a signature of quiet a variety of disorderd media, it seems straightforward to also look into nanglasses and figure out whether or not the universal viscoplastic material response prevails.