Synergistic effect of carbon nanotube as sintering aid and toughening agent in spark plasma sintered molybdenum disilicide-hafnium carbide composite

Densification, strengthening and toughening in hafnium carbide with the addition of silicon carbonitride

“…The addition of SiC in HfC has been shown to increase material strength, 6,7 while carbon has an opposite effect. 11 In the current system, when the SiCN content increases, the hardness of the sample decreases monotonically although the amount of harder SiC and softer carbon phases both increase, which suggests that overall the softening effect of carbon surpasses the hardening effect of SiC and grain refinement. Therefore, the strength is a trade-off between composition and microstructure and a function of the SiCN content.…”

“…6,7 Carbon and carbon-based nanostructures (CNTs, graphene) have shown interesting effect in the fracture toughness. [11][12][13] While the addition of 5.0 vol% carbon black only increases the fracture toughness by ~25% in ZrB 2 -SiC composites, 14 adding similar volume content of CNTs and graphene showed a greater improvement of 83%-130% for the fracture toughness in HfC-MoSi 2 or ZrB 2 . [11][12][13] Mukherjee et al 11 investigated the CNTs-HfC-MoSi 2 composites system, of which K IC was improved from 3.1 to 5.9 MPa m 1/2 with the presence of 2.0 wt.% CNTs.…”

High fracture toughness of HfC through nano‐scale templating and novel sintering aids

“…% SiCN sintering aid possesses a unique composite structure where multiple phases with graded hardness form a uniform inter‐penetrating 3D network at multi‐length scales. This HfC ceramic sample shows a higher fracture toughness (5.5 MPa m 1/2 ) than that of the reported isotropic HfC samples . This preferable microstructure plays a significant role in crack deflection, bridging and arrest, promoting the stress release in the crack tip.…”

“…HfC–W cermets have a high fracture toughness of 13.7 ± 0.7 MPa m 1/2 , but at a cost of a higher weight and a lower ablation resistance . Carbon nanotubes (CNTs) have also been incorporated into HfC–MoSi 2 and SiC–ZrB 2 composites as a toughening phase, respectively. However, CNTs can react with ceramic matrix and form a strong interfacial bonding, which is unfavorable for high toughness.…”

“…The fabrication of nanopowders and the addition of sintering aids are common approaches to enhance the sintering ability of ceramics. Nano carbon allotropes, disilicides or other carbides used as sintering aids have been reported for sintering of HfC . However, the introduction of these sintering aids have been found to also result in unfavorable microstructure changes, such as abnormal grain growth or formation of different surface defects on HfC grains with fast diffusion and mass transfer rate, which are detrimental to the intrinsic properties of HfC, such as high thermodynamic stability, melting point, and good thermomechanical, as well as contribute to the limited fracture toughness of 2.8‐4.0 MPa m 1/2 reported for the sintered material .…”