Densification mechanism of spark plasma sintered ZrB2 and ZrB2-SiC ceramic composites

Abstract

Sintering mechanisms are investigated by determining activation energy of densification (in the temperature range of 1650 °C to 1950 °C) during spark plasma sintering of ZrB2 and SiC-reinforced ZrB2 ceramic composite. The fractured surfaces of sintered composites reveal completely dense microstructures above 1800 °C, whereas porous microstructure prevailed in ZrB2 even after sintering at 1950 °C. Activation energy of 80 ± 16 kJ/mol is obtained for ZrB2 with grain boundary diffusion as governing diffusion mechanism in the temperature range of 1650 to 1950 °C. On the other hand, dominant densification mechanism of grain boundary diffusion (activation energy of 89 ± 19 kJ/mol) estimated in the range of 1650 to 1800 °C changed to lattice diffusion (activation energy of 601 ± 10 kJ/mol) with the addition of 20 vol% SiC in ZrB2. The change of prominent densification mechanism in ZrB2 with SiC, in addition to its impact on the mechanical performance with systemic increase of sintering temperature, is unravelled here.