  The thermal decomposition behavior, the microstructural evolution and its
influence on the mechanical properties of a supersaturated Cu Co solid solution
with ~100 nm average grain size prepared by severe plastic deformation is
investigated under non-isothermal and isothermal annealing conditions. Pure
fine grained Cu and Co exhibit substantial grain growth upon annealing, whereas
the Cu Co alloy is thermally stable at the same annealing temperatures. The
annealed microstructures are studied by independent characterization methods,
including scanning electron microscopy, electron energy loss spectroscopy and
atom probe tomography. The phase separation process in the Cu Co alloy proceeds
by the same mechanism, but on different length scales: a fine scaled spinodal
type decomposition is observed in the grain interior, simultaneously Co and Cu
regions with a larger scale are formed near the grain boundary regions.
Subsequent grain growth at higher annealing temperatures results in a
microstructure consisting of the pure equilibrium phases. Such mechanisms can
be used to tailor nano structures to optimize certain properties.
