Processing of orthotropic and isotropic superhard B4C composites reinforced with reduced graphene oxide

A fabrication route based on aqueous colloidal processing plus transient liquid-phase assisted spark-plasma-sintering (SPS) with Ti-Al additives is described for the environmentally friendly obtention of superhard B4C composites reinforced with reduced graphene oxide (rGO) having orthotropic and isotropic microstructures. It is shown that the former, which have coarse rGO platelets preferentially aligned perpendicular to the SPS pressing direction, can be prepared from mixtures of B4C and Ti-Al particles with a source of thick, large rGO nanoplatelets by imposing smooth co-dispersion conditions to avoid platelet re-exfoliation and fragmentation. The latter, which have fine rGO platelets randomly oriented, can be fabricated from mixtures of B4C and Ti-Al particles with a source of thin, small rGO nanoplatelets by applying intensive sonication to promote platelet re-exfoliation and fragmentation during co-dispersion. Finally, it is shown that these orthotropic and isotropic B4C/rGO composites are equally superhard, and that, as expected, their microstructures interact differently with the cracks. Finally, this processing route is simple, and easily adaptable/extensible to make other ceramic/rGO composites with orthotropic and isotropic microstructures.