(Ta,Nb)C composites formed with graphene nanoplatelets by spark plasma sintering

TaC-NbC with the addition of sintering additive (5 vol.% B4C or 5 vol.% Si) and 3 vol.% Graphene Nanoplatelets (GNP) are consolidated by spark plasma sintering (SPS). GNP are aligned in a uniformly oriented direction perpendicular to the processing axis of the SPS equipment during consolidation. High load instrumented indentation is performed and the projected area of residual damage is compared to estimate relative fracture toughness. The projected residual damaged area after indentation in the surface direction (out-of-plane GNP orientation) was 89% greater in the TaC-NbC-5B4C-3GNP sample, and 96% greater in the TaC-NbC-5Si-3GNP sample when compared to indentation in the orthogonal (in-plane GNP orientation) direction. The toughening mechanisms prevalent in the orthogonal indentation direction (crack bridging and crack deflection) result in greater energy dissipation than the prevalent mechanisms in the surface indentation orientation (sheet sliding, crack bridging, and crack arrest).