Evolution of the lattice defects and crystalline domain size in carbon nanotube metal matrix composites processed by severe plastic deformation

Nickel (Ni) and carbon nanotube (CNT)-reinforced Ni-matrix composites were processed by high-pressure torsion (HPT). The evolution of dislocation densities and crystalline domain sizes were analyzed by means of X-ray diffraction (XRD) using Whole Powder Pattern Modelling (WPPM). The composites showed an evident gradient in the microstructural refinement and in hardness with increasing applied strain. This effect was found to be more pronounced in the presence of higher amounts of CNT. In particular, a higher amount of screw dislocations was measured by WPPM after HPT. It was concluded that the strengthening of CNT-MMC processed by HPT is mainly due to work hardening and grain refinement, both mechanisms being assisted by the presence of CNT, with marginal contribution of particle strengthening.