From our experiments, we found that the toughness of ultrahard material such as WC, SiC, can be improved by adding a little CNTs or graphene and sintering them together.
WC is a popular ultrahard material used as a mold material. There are two types of WC mold: Cobalt-free and Cobalt added as binder. In the case Co-free, the hardness is perfect but the toughness will decay much. In the case of Co-added, the hardness will decay but the toughness is much improved.
We have added a small amount of CNTs to both cases of Co-free and Co-added and we found that the toughness of the sintered compact of each case gets better. We do not yet understand the mechanism of the toughness-improvement effect by CNTs, but we suppose that CNTs may stop the progress of cracking.
Furthermore, addition of CNTs or graphene to metals or ceramics may improve also the thermal conductivity of sintered compact. We can provide original CNT-added compact by using our SPS machines for sintering metals or ceramics materials.