X-Ray Diffraction Studies of Forward and Reverse Plastic Flow in Nanoscale Layers During Thermal Cycling

Abstract

The biaxial stress–strain response of Cu and Ni layers within Cu/Ni nanolaminates was determined from in-plane X-ray diffraction during heating/cooling. Thinner (11 nm) Cu and Ni layers with coherent, cube-on-cube interfaces reached ∼1.8 GPa (Cu) and ∼2.9 GPa (Ni) without yielding. Thicker (21 nm) layers with semi-coherent interfaces exhibited unusual plastic phenomena, including extraordinary increases in stress during early yielding, reverse plastic flow at modest (∼12%) unloading and evidence that plastic flow in Cu layers can reduce the flow strength of adjoining Ni layers. Estimates of dislocation line energy, pinning strength, net interfacial dislocation density and hardness are provided.

Keywords:

• Nanolaminates
• X-Ray Diffraction
• Interface Properties

The authors gratefully acknowledge discussions with Prof. William. D. Nix (Stanford), fabrication of the multilayer thin films by J. Kevin Baldwin (LANL), and TEM assistance from Matthew L. Bowers (OSU). This work was supported by the National Science Foundation (Division of Materials Research DMR-0907024, Diana Farkas, Program Officer). This research was conducted at the CNMS, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy and by the CINT, a US Department of Energy, Office of Basic Energy Sciences user facility at Los Alamos National Laboratory (Contract DE-AC52-06NA25396) and Sandia National Laboratories (Contract DE-AC04-94AL85000).