Combined and alone addition effect of nano carbon black and SiC on the densification and fracture toughness of SPS-sintered ZrB2

ZrB2-nano-size carbon black (C.Bn), ZrB2-SiC, and ZrB2-SiC-C.Bn specimens were fabricated by spark plasma sintering (SPS) at 1850 °C for 8 min under 35 MPa pressure. The bulk density (B.D) was measured by the Archimedes method. The single-edge notched beam (SENB) method was applied to investigate the fracture toughness and work of fracture (WOF). It was found that the combined addition of C.Bn and SiC modified the densification behavior to reach full-densified samples. Also, it was found that the fracture toughness and WOF were improved by the addition of C.Bn to the monolithic ZrB2 continuously, and they reached 5.1 ± 0.1 MPa·m1/2 and 433 ± 20 J·m−2, respectively for the sample containing 15 vol% C.Bn. Compared to monolithic ZrB2, the fracture toughness and the WOF for the composite with 30 vol% SiC and 15 vol% C.Bn increased nearly 26 % and 57 %, respectively. It was noteworthy that the alone addition of C.Bn to the pure ZrB2 had more effect in improving the fracture toughness than the simultaneous addition of C.Bn and 30 vol% SiC. The predominant mechanisms in fracture toughness improvement can be related to the observed crack deflections, branching, and bridging in scanning electron microscopy (SEM) images.