Metallic nanolayered composites exhibit ultra-high strength and ductility

Some of the challenges in evaluating the stress-strain response of nanomaterials involve the fabrication of flaw-free samples that will reliably give mechanical test data reflecting the bulk material properties independent of geometric effects of sample size or embedded flaws. Magnetron sputtering at the Center for Integrated Nanotechnologies provides for fabrication of metallic multilayers such that (i) the growth-induced residual stresses and flaws/porosity are minimized, (ii) the individual layer thicknesses are well-controlled in the nanometer range, and (iii) the overall sample thickness is sufficient to make self-supported foils. This precise control over length scales allows for systematic investigation of the effects of increasing the amount of interfacial content on material behavior. Figure 1 is a cross-sectional transmission electron micrograph (TEM) of a sample with 5-nm layer thickness, although layers of alternating Cu and Nb can be easily varied in thickness to investigate length scales (and accompanying deformation mechanisms) from hundreds of nanometers to ~1 nm in samples with identical chemical composition. The laminar nature of the composites is evident from the micrograph, with the (111) planes of fcc-Cu and (110) planes of bcc-Nb forming the interface between the two phases, as shown in the diffraction pattern embedded selected area. Once deposited, nanolayered composites can be deformed utilizing a variety of methods, including rolling2, tension3, indentation4, or as in this case, micropillar compression. Focused ion beam (FIB) machining has opened opportunities for fabrication of micropillar samples, where a Ga+ ion beam is used to remove material to shape a sample to high precision.5,6 The inset scanning electron microscopy (SEM) micro-graph in Figure 2 shows such a pillar with nominal dimensions of a diameter of 4µm and a height of 8µm. The layer direction is perpendicular to the cylinder axis, M