Ultrahigh hardness on a face-centered cubic metal

Abstract

Nanotwinned (NT) surfaces are developed on a face-centered cubic (fcc) metal with ultrahigh hardness under cyclic loading using plastic deformation at room temperature. The hardness on NT surfaces remains constant at 7.9 and 8.5GPa indented at 1 and 7N under 0–100 cycles respectively, which are about three times that of their pristine surfaces. This is different from the NT metals and nonmetallic materials, on which the hardness is about two times that of their pristine counterparts. Moreover, NT metals usually consist of randomly oriented twin and grain boundaries, making it difficult to control the uniform mechanical property. Here, novel nt structure is proposed on an fcc metal, in which all the twin boundaries are along (-1-11) orientation, forming bundles of nanotwins to several micrometers in length.