Size-Dependent Strength in Single-Crystalline Metallic Nanostructures

Abstract

The emergence of a substantial body of literature focusing on uniaxial compression experiments of micro- and nano-sized single-crystalline cylindrical papers has unambiguously demonstrated that, at these scales, the sample dimensions dramatically affect crystalline strength (for reviews, see [1-3]). In most of these experimental studies, cylindrical pillars with diameters ranging from ~ 100 nm up to several micrometers were fabricated, largely by the use of the focused ion beam (FIB) method, with some non-FIB-based methods as well, and were subsequently compressed in a nanoindenter with a custom-made flat punch indenter tip. More recently, small-scale mechanical behavior has also been explored through uniaxial tensile experiments, usually performed inside of in-situ scanning electron microscopes (SEM)- or transmission electron microscopes (TEM)-with the custom-built mechanical deformation instruments by a small number of research groups [3-6]. Intriguingly, the results of all of these reports for single-crystalline metals with a variety of crystal structures - face-centered cubic (fcc), body-centered cubic (bcc), hexagonal close-packed (hcp), and tetragonal -show power-law dependence between flow stress and pillar diameter. Further, within the fcc family, the slopes of all metals tested converge on a unique value of approximately -0.6 [1-3,7] (see Figure 7.1), which is not the case for all other crystals.

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