The strength of nanocrystalline metals with and without flaws

The expectation of large grain-boundary strengthening and extensive grain-boundary sliding has motivated a number of studies of the mechanical properties of nanocrystalline metals. However, poor sample quality frequently has led to results that are far removed from the actual mechanical behavior of the flaw-free material. Several examples, involving elastic moduli, hardness, and yield strength, are given. Recent tests in compression of high density nanocrystalline metals have shown high hardness and yield strength values that are compatible with extrapolation of coarse-grain Hall-Petch data to the nanocrystalline regime.