Synthesis of the ZrN–ZrB2 Composite by Spark Plasma Sintering

Reactive spark plasma sintering of ZrH2, BN, and B powder mixtures in the temperature range 1500–1900°C was used to produce a ZrN–ZrB2 ceramic composite with 35–80 wt.% ZrB2. The phase transformations in the temperature range 900–1900°C, the nature of densification at 1800°C, and the effect of composition and sintering temperature on the mechanical properties of the sintered composites were examined. The densification process occurs in four stages at a sintering temperature of 1800°C. At the first sintering stage, ZrH2 starts dehydrogenating with the release of atomic (molecular) hydrogen (before the time dependence of shrinkage becomes S-shaped). The second stage involves chemical reactions in the system. At the third and fourth stages, synthesized ZrN and ZrB2 are sintered directly. The zirconium–boron interaction proceeding through selfpropagated high-temperature synthesis influences the densification and final structurization of the composites. As a result, the highest mechanical properties are exhibited by the samples with 80 wt.% ZrB2 sintered in the range 1800–1900°C.