Thermal stability of Cu–Nb nanolamellar composites fabricated via accumulative roll bonding

Abstract

In situ annealing within a neutron beam line and ex situ annealing followed by transmission electron microscopy were used to study the thermal stability of the texture, microstructure, and bi-metal interface in bulk nanolamellar Cu/Nb composites (h = 18 nm individual layer thickness) fabricated via accumulative roll bonding, a severe plastic deformation technique. Compared to the bulk single-phase constituent materials, the nanocomposite is two orders of magnitude higher in hardness and significantly more thermally stable, e.g., no observed recrystallization in Cu at temperatures as high as 85% of the melting temperature. The nanoscale h = 18 nm individual layer thickness is maintained up to 500°C, the lamellar structure thickens but is maintained up to 700°C, and recrystallization is suppressed even up to 900°C. With increasing temperature, the texture sharpens, and among the interfaces found in the starting material, the {112}_Cu|| {112}_Nb interface with a Kurdjumov-Sachs orientation relationship shows the greatest thermal stability. Our results suggest that thickening of the individual layers under heat treatment coincides with thermally driven removal of energetically unfavorable bi-metal interfaces. Thus, we uncover a temperature regime that maintains the lamellar structure but alters the interface distribution such that a single, low energy, thermally stable interface prevails.

Keywords:

• thermal stability
• nanocomposites
• metals
• neutron diffraction

Acknowledgments

The authors are grateful for valuable discussions with Prof. A.D. Rollett of Carnegie Mellon University and Dr. K. W. Kang of Los Alamos National Laboratory. The authors also acknowledge Dr. J.C. Cooley of Los Alamos National Laboratory for his expertise and the use of his drop furnace. This work was funded through Los Alamos National Laboratory Directed Research and Development Project DR20110029 and by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Energy Frontier Research Center under Award No. 2008LANL1026. This work has benefited from the use of the Lujan Neutron Scattering Center at LANSCE, which is funded by the Office of Basic Energy Sciences (DOE). Los Alamos National Laboratory is operated by Los Alamos National Security, LLC under DOE Contract DE AC52 06NA25396. This work was performed, in part, at the Center for Integrated Nanotechnologies, 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).