LI Jia ¹, WEI Hongkang ¹, QIU Huijuan ¹, XIE Zhipeng ^{1, 2}, WANG Chang’an ^{1, 2}, ZHAO Lin ¹

(1. Jingdezhen Ceramic University, Jingdezhen 333403, Jiangxi, China; 2. State Key Laboratory of

New Ceramics and Fine Processing, Tsinghua University, Beijing 100084, China)

Extended abstract:[Background and purposes] Due to its high hardness, high thermal conductivity, outstanding corrosion resistance and strong chemical stability, silicon carbide (SiC) has been widely used in high-tech material manufacturing fields, such as aerospace, national defense, nuclear industry and space technology. Nevertheless, the high hardness and brittleness of SiC ceramics render them extremely difficult to be processed into complex shapes by using the traditional mechanical processing techniques. Introducing a second phase with high mechanical properties and high electrical conductivity into the silicon carbide matrix is considered as an effective approach to enhance the comprehensive and processing performances of SiC ceramics.[Methods] SiC-TiB₂-ZrN composite ceramics were prepared by using β-SiC, ZrB₂ and TiN as the raw materials at 2000 ℃ and 40 MPa. The effects of the content of the additives on phase composition, microstructure, mechanical properties and electrical conductivity of the SiC-based composite ceramics were studied. ZrB₂ and TiN reacted in-situ to form TiB₂ and ZrN. The in-situ reaction improved the sintering performance of SiC ceramics. The generated TiB₂ and ZrN possess excellent electrical conductivity and mechanical properties, thus significantly improving the electrical conductivity and mechanical properties of the final products.[Results] SiC-TiB₂-ZrN composite ceramics were obtained from the raw materials with different formulations, while no ZrB₂ and TiN residues were retained after sintering. During the sintering process, the generated TiB₂ and ZrN were mutually dissolved, causing the XRD diffraction peaks of the two phases to shift. With increasing content of the additive, the porosity of the ceramic composites decreased from 12.96% to 0.07%, indicating that the in-situ reaction of ZrB₂ and TiN significantly enhanced the sintering activity of SiC. When the contents of TiB₂ and ZrN were 30 mol%, the hardness and fracture toughness of the ceramic composites ceramics were 25.19 GPa and 5.68 MPa·m^1/2, respectively. The SiC grains experienced transgranular fracture mode dominantly. The presence of TiB₂ and ZrN in the ceramic composites leads to the occurrence of intergranular fracture mode. Moreover, when the cracks propagated in TiB₂ with higher mechanical properties, the crack propagation path was significantly tortured. Electrical conductivity of the ceramic composite with 30 mol% TiB₂ and ZrN was 3.3×10³ Ω⁻¹·cm⁻¹.

[Conclusions] SiC-TiB₂-ZrN ceramic composites were successfully fabricated using β-SiC, ZrB₂ and TiN as raw materials. The TiB₂ and ZrN phases in the ceramic composites inhibited the phase transformation of β-SiC to α-SiC. The addition of additives was beneficial to densification and mechanical properties of the SiC ceramic composites. When the contents of TiB₂ and ZrN were 30 mol%, the apparent porosity, Vickers hardness and fracture toughness of SiC ceramic composites were 0.07%, 25.19 GPa and 5.68 MPa·m^1/2, respectively. The improvement of mechanical properties was attributed to the increase in density and the change in fracture mode. Due to the high electrical conductivity of TiB₂ and ZrN and their inhibition of the crystal phase transformation of β-SiC, the STZ30 sample had high electrical conductivity of 3.3×10³ Ω⁻¹·cm⁻¹,making the SiC-TiB₂-ZrN ceramic composites suitable for EDM processing technology, which has advantages in improving processing efficiency and realization of complex shapes.

Key words: SiC-TiB₂-ZrN ceramic composites; mechanical properties; conductivity performance; phase evolution; microstructure