Transient liquid-phase assisted low-temperature spark plasma sintering of TiCN with Si aids

The feasibility of densifying TiCN at a much lower temperature than currently by using transient liquid-phase assisted spark plasma sintering (SPS) with Si aids is demonstrated. Firstly, it is shown that TiCN can be fully densified by SPS at 1400 degrees C with only 5 vol% Si aids, a temperature at which TiCN hardly densifies at all, resulting in novel superhard (similar to 21.5 GPa) ceramic composites having fine-grained (<1 m) multi-particulate microstructures with TiCN as the main phase and SiC, TiSi2, and TiN as secondary phases. It is found that all this is because Si is a reactive sintering aid (2TiC(0.5)N(0.5)+3Si -> SiC+TiSi2+TiN) and because during SPS two eutectic melts are formed, first a Si-rich one at similar to 1275 degrees C and then a TiSi2-rich one at similar to 1375 degrees C. Secondly, it is shown that TiCN can also be fully densified by SPS at only 1275 degrees C with 5 vol% Si aids, giving the same superhard ceramic composites as at 1400 degrees C, but requiring much longer holding because only the Si-rich eutectic melt is formed. And thirdly, it is shown that the densification of TiCN+Si is more favoured with increasing vol% Si aids, which is important for its pressureless sintering, and also that these superhard multi-particulate TiCN-based composites are slightly less hard but slightly tougher and lighter the more SiC, TiSi2, and TiN secondary phases are formed in situ during SPS by the reaction between TiCN and Si.