Fabrication of Cu-based metal matrix composites reinforced with carbon nanofillers

The thesis takes inspiration from the worldwide issues related to the shortage of critical raw materials (CRMs) and the need of finding sustainable alternatives to CRMs within fields and sectors strategic to the well-being and economy of industrialized countries. The research activity has been focused on the fabrication of Cu-matrix composites reinforced with carbon nanofillers, nano-graphite and graphene in particular. This class of composites attracts considerable interest as a consequence of the broad spectrum of applications Cu-MCs could find due to their thermal and electric conductivities, self-lubricating properties of graphite, cost-effectiveness and availability. Ball milling (BM) and spark plasma sintering (SPS) have been combined to provide an innovative methodology to fabricate Cu-MCs reinforced with carbon nanofillers enabling the fine dispersion of nanoparticles into the Cu matrix. Specifically, a two-stage cycle involving BM first and, then, SPS has been shown to result in the dispersion of graphite particles in relatively large Cu grains. The iteration of cycles allows the refinement of graphite nanoparticles and their dispersion in Cu powders on the microscopic scale, mostly at grain boundaries, and the subsequent incorporation of nanoparticles into Cu grains due to grain growth mechanisms activated and promoted by high temperatures during SPS. Molecular level mixing has been also tested to obtain Cu-MCs reinforced with graphene starting from liquid solutions of Cu nanoparticles and graphene. In particular, graphene was dispersed during the redox synthesis to obtain Cu nanopowder, subsequently consolidated by SPS. Despite the intrinsic different between the two methods, it has been possible to prepare Cu-MCs with graphite nanoparticles and graphene as dispersoids. Structural and microstructural characterization indicate that dispersoids are finely dispersed into the Cu matrix. Nanoindentation measurements clearly demonstrate the significant enhancement of mechanical properties, thus providing an important clue to the validity of the methodology developed.