  The mechanical properties and deformation mechanisms of Cu/Nb nanoscale
metallic multilayers (NMMs) manufactured by accumulative roll bonding (ARB) are
studied at 25C and 400C. Cu/Nb NMMs with individual layer thicknesses between 7
and 63 nm were tested by in-situ micropillar compression inside a scanning
electron microscope Yield strength, strain-rate sensitivities and activation
volumes were obtained from the pillar compression tests. The deformed
micropillars were examined under scanning and transmission electron microscopy
in order to examine the deformation mechanisms active for different layer
thicknesses and temperatures. The analysis suggests that room temperature
deformation was determined by dislocation glide at larger layer thicknesses and
interface-related mechanisms at the thinner layer thicknesses. The high
temperature compression tests, in contrast, revealed superior thermo-mechanical
stability and strength retention for the NMMs with larger layer thicknesses
with deformation controlled by dislocation glide. A remarkable transition in
deformation mechanism occurred as the layer thickness decreased, to a
deformation response controlled by diffusion processes along the interfaces,
which resulted in temperature-induced softening. A deformation mechanism map,
in terms of layer thickness and temperature, is proposed from the results
obtained in this investigation.
