Reactive sintering of TiB2-SiC-CNT ceramics

Abstract

TiB2-SiC ceramics with multi-wall carbon nanotubes (MW-CNT) were reactively hot pressed at 1800°C and 30 MPa. Carbon nanotubes survived the process and could be clearly observed in the sintered ceramics. The in-situ exothermic reactions between TiC, B4C and Si accelerated the densification and produced nonporous TiB2-SiC ultrahigh-temperature ceramics within one minute at 1800 °C. Although the toughness of the ceramic was not significantly affected by the CNT addition, remaining around 6 MPa•m 1/2 , the CNT presence resulted in a substantial improvement in TiB2-SiC thermal shock resistance. The Vickers hardness decreased from 27GPa for the CNT-free matrix to 21GPa for ceramic with maximum CNT content (7.4 wt.%).

Reactive hot pressing route for dense ZrB2-SiC and ZrB2-SiC-CNT ultra-high temperature ceramics

“…2) proceeds via two densification waves starting at 1000 °C and 1500°C with maximum densification rates of 1 and 1.4 mm/min respectively and no visible shrinkage between 1300°C and 1500°C. The results correlate well with those reported for the TiC-B4C-Si system [26]. However, in contrast to the TiC-B4C-Si system, the densification rate in the second stage is essentially higher than in the first stage and the shrinkage plateau is longer in the ZrC-B4C-Si system.…”

“…The consolidation plateaus. The shrinkage plateau similar to the one between 1250 and 1500 °C observed in the TiB2-SiC-CNT system [26] was attributed to the reaction deceleration. The reaction product accumulation could retard further interaction.…”

“…Our latest results, concerning the reactive hot pressing of a TiB2-SiC-CNT composite [26] have demonstrated carbon nanotube survival in a TiB2-SiC matrix. The reaction products were the same as in ( 1), but based on a metal carbide instead of pure metal starting powder.…”

“…Reaction ( 2) is based on the interaction between metal carbide and boron carbide, for which successful reaction synthesis during hot pressing of titanium and hafnium based systems has been reported [27]. The chemical similarity of ZrC with TiC and HfC allows to assume that the reaction (2) path will be similar to that presented in [26]. The current work addresses the reactive hot pressing of ZrB2-SiC ultra-high temperature ceramics according to reaction (2).…”

Pulsed electric current sintering of TiB2-based ceramics using nitride additives

“…However, this notable substance had some demerits, e.g. low self-diffusion coefficient, surface oxide layers (TiO 2 , B 2 O 3 ), and strong covalent bonding, which make its sinterability problematic [8][9][10]. According to the previous studies, reaching a near fully dense TiB 2 material needs both a high sintering temperature and a very high external pressure (~3 GPa).…”