Deformation crossover in nanocrystalline Zr micropillars: The strongest external size

For small-scale metallic single crystals, systematic studies have established that external sample size (ϕϕ) has an obvious influence on the apparent strength, following a “smaller is stronger” fashion. In the present nanocrystalline (NC) Zr micropillars, deformation crossover leads to the strongest external size emerging at a critical ϕ≈400nm, similar to that of bulk-scaled NC metals. Above the critical external size the NC Zr pillars failed via highly inhomogeneous single-shear offset, below which they deformed via relative homogeneous shear.