SYNTHESIS OF THE ZrN–ZrВ₂ COMPOSITE BY SPARK PLASMA SINTERING

Abstract

Reactive spark plasma sintering of ZrH₂, BN, and B powder mixtures in the temperature range 1500–1900 ºC was used to produce a ZrN–ZrВ₂ ceramic composite with 35–80 wt.% ZrВ₂. The phase transformations in the temperature range 900–1900 ºC, the nature of densification at 1800 ºC, and the effect of composition and sintering temperature on the mechanical properties of the sintered composites were examined. The densification process proceeds in four stages at a sintering temperature of 1800 ºC. At the first sintering stage, ZrH₂ dehydrogenation begins with the release of atomic (molecular) hydrogen (before the time dependence of shrinkage becomes S-shaped). The second stages 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 self-propagated 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 ºС.