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

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We studied solid solution effects on the mechanical properties of nanocrystalline (NC) Pd₁₀₀₋ₓ Auₓ alloys (0 ≤ x < 50 at.%) 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≈ 10 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)].