Anomalies in Hall-Petch strengthening for nanocrystalline Au-Cu alloys below 10 nm grain size

The mechanical behavior of an electrodeposited nanocrystalline alloy is assessed with regards to the experimentally measured strain-rate sensitivity. Foils are characterized with grain sizes as small as 3 nm, a nano-scale regime that has previously gone without detailed experimental examination. It is found from micro-scratch measurements that hardness, hence strength, approaches ideal values as the grain size decreases to 7 nm. Below 7 nm, softening in strength and departure from Hall-Petch behavior is related to an increase in the activation volume for deformation as grain size decreases further.