Enhanced tensile strength of nanotwinned nanoporous gold

Abstract

Twin boundaries are effective microstructural defects for enhancing the strength of materials at multiple scales. Twin boundaries are mirror planes in the crystallographic lattice with perfect coherency and serve as strong barriers to dislocation motion and slip transfer, resulting in high strength. The mechanical fragility of np-Au is fundamentally attributable to its low tensile strength, which is caused by its irregular open-cell structures and results in catastrophic failure under tension. Stress gets concentrated at the weak parts of the load-bearing ligaments when the material is subjected to an external tensile force. Thus, strength of np-Au could get increased by enhancing yield stress of load-bearing ligaments with introducing nanotwin structure in ligaments. We fabricated nanotwinned nanoporous gold (nt np-Au) thin film and measured its mechanical properties using in-situ tensile testing. We fabricated twinned and textured np-Au foils with an average twin spacing of 7.9 nm. The foils exhibit an ultimate tensile strength (UTS) of 87.5MPa when the loading axis is normal to the twin boundaries. This UTS value is approximately three times greater than that for np-Au with rare twins of 27.4 MPa due to strain-hardening of nanotwin barriers in load-bearing ligaments.