  In this work we use density functional theory (DFT) calculations to benchmark
empirical potentials for the interaction between nickel and sp$^2$ bonded
carbon nanoparticles. These potentials are then used in order to investigate
how Ni decorated or coated carbon nanotubes (CNT) affect the mechanical
properties of Al/CNT composites. In particular we look at the pull-out
behaviour of pristine as well as Ni-decorated and Ni-coated CNT from an Al
matrix. Our result shows that Ni coating may produce an extended interface
(interphase) where a significant amount of energy is dissipated during CNT
pull-out, leading to a high pull-out force. We also demonstrate that surface
decorated CNT may act as efficient nano-crystallization agents and thus provide
a novel strengthening mechanism not previously discussed in the literature. We
discuss our results in view of promising approaches for engineering CNT-metal
interfaces such as to achieve high strength metal-CNT composite.
