Plastic yielding in nanocrystalline Pd-Au alloys mimics universal behavior of metallic glasses

Abstract

We studied solid solution effects on the mechanical properties of nanocrystalline (NC) ${\mathrm{Pd}}_{100-\mathrm{x}}{\mathrm{Au}}_{\mathrm{x}}$ alloys ($0\le \mathrm{x}<50at.\%$) at the low end of the nanoscale. Concentration has been used as control parameter to tune material properties (elastic moduli, Burgers vector, stacking fault energies) at basically unaltered microstructure (grain size $D\approx 10\mathrm{nm}$). In stark contrast to coarse grained fcc alloys, we observe solid solution softening for increasing Au-content. The available predictions from models and theories taking explicitly into account the effect of the nanoscale microstructure on the concentration-dependent shear strength have been disproved without exception. As a consequence, it is implied that dislocation activity contributes only marginally to strength. In fact, we find a linear correlation between shear strength and shear modulus which quantitatively agrees with the universal behavior of metallic glasses discovered by Johnson and Samwer [W.L. Johnson and K. Samwer, PRL 95, 195501 (2005)].

10 pages, 7 figures, revised manuscript accepted by PRB