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

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=18nm 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=18nm individual layer thickness is maintained up to 500 degrees C, the lamellar structure thickens but is maintained up to 700 degrees C, and recrystallization is suppressed even up to 900 degrees 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.