  Carbon nanotubes (CNT) have been recently proposed as stabilizers against
grain growth that can happen even at low temperature inputs in nano-crystalline
and ultrafine-grained materials obtained by severe plastic deformation. In this
study, we analyzed the evolution of the structural defects on the nanotubes in
CNT-reinforced nickel matrix composites with different reinforcement weight
fractions. The composites were processed by high pressure torsion, and we used
Raman spectroscopy as the main characterization technique. The results indicate
that for CNT subjected to highly energetic processing, it is not sufficient to
analyze only the ID/IG ratio (as proposed in the available literature), but it
is also necessary to evaluate the shifting of the G band, which traces the
amorphization trajectory undergone by the CNT. Furthermore, we observed that
the deformation suffered by the CNT is related to the accumulated strain and
varies with the partial CNT fractions of these composites. This is related to
their capacity to withstand the plastic strain that occurs during deformation.
In addition, the defective state reaches a saturation before achieving the
saturation in the microstructural refinement. These results will help to
efficiently optimize the processing of this type of engineering composites.
