The microstructural parameters of the Cu matrix in the cryorolled
sample were obtained by XLPA. The crystallite size in the
as-rolled condition (30 nm) is much smaller and the dislocation
density is significantly higher (48 1014 m2) than the values
reported in pure Cu processed by different SPD methods [28–30].
This observation can be explained by the pinning effect of Ag on
dislocations and grain boundaries formed during SPD and the
low temperature of deformation (LNT). The twin boundary probability
was 0.5 ± 0.1%. The UFG microstructure in the rolled material
is illustrated in the TEM image of Fig. 2a taken in the RD-TD plane
(RD: rolling direction, TD: transverse direction). It should be noted
that the grain size is much larger than the crystallite size obtained
by XLPA which is in accordance with earlier studies and can be
explained by the fact that the crystallite size usually corresponds
to the subgrain size in severely deformed microstructures [31].
The dark-field TEM image in Fig. 2b was obtained for the cryorolled
sample using an Ag reflection. In this area the Ag precipitates
are equiaxed with the size of a few nanometers