Reactive spark plasma sintering of ZrB۲-TiC composites: Role of nano-sized carbon black additive

ZrB۲-TiC composites with and without nano-sized carbon black as the sintering additive were densified through spark plasma sintering at ۱۹۰۰ °C for ۷ minutes under the applied pressure of ۴۰ MPa. The role of carbon black in densification behavior, phase arrangement, microstructural characteristics and mechanical properties of the sintered composites were then investigated. While both of the composite samples were found to be fully sintered, the thermodynamic of the reactive sintering was also studied. The results indicated that whereas the reactive sintering process leads to the complete consumption of TiC through the formation of the solid solution as the matrix in both of the composite samples, the presence of carbon black at the initial composition of the samples can result in remained carbon at the final microstructure. Besides the in-situ synthesized zirconium carbide as the major reinforcement phase, such a remained carbon can lead to significantly different mechanical behavior of the composites. Accordingly, the hardness of ۲۱.۸ and ۲۴.۳ GPa and the indentation fracture toughness of ۳.۳ and ۴.۵ MPa.m۰.۵ were obtained for carbon-black free and doped samples, respectively. The densification, hardening, and toughening mechanisms in both of the composite samples were finally discussed.

Keywords:

Spark plasma sintering , Zirconium diboride , Titanium carbide , In-situ synthesis , Toughening mechanism