Spark plasma sintering of hard wear-resistant graphene nanoplatelet–reinforced TiB2 + SiC composites from TiC–B4C–SiC

Graphene nanoplatelet (GNP)–reinforced TiB₂ + SiC composites were fabricated by reactive spark plasma sintering (SPS) from a TiC–B₄C–SiC powder mixture with equal-volume percentages, optimizing their SPS temperature and evaluating their unlubricated sliding wear against diamond. First, it is shown that during the heating ramp of the SPS cycle, TiC and B₄C react according to the chemical reaction 2TiC + B₄C → 2TiB₂ + 3C, and that the thus-formed C is graphenized as GNPs, leading to composites with microstructures consisting of a ceramic matrix of fine TiB₂ and SiC grains with abundant randomly oriented GNPs at grain boundaries. It is also shown that this reactive SPS is optimal at 2000°C (under 75 MPa pressure and 5 min soaking), resulting in a very hard (∼28.5–29.9 GPa) and very tough (∼6.7(3) MPa m^1/2) composite. And second, it is shown that these two properties and its proneness to develop an oxide tribolayer make this composite very resistant to unlubricated sliding wear against diamond (∼2.8(1)·10⁸ (N m)/mm³), undergoing only very mild two-body abrasion. Finally, opportunities for the fabrication of toughened and very hard ceramic composites for contact-mechanical and tribological applications are discussed.