Fabrication And Properties Research Of SiC-TiB₂ Multiphase Ceramics

Silicon carbide?SiC?has been widely used in machinery,chemical engineering and armor application due to its excellent properties such as high hardness,good oxidation resistance and good thermal shock resistance.However,the application of SiC ceramic is limited by its poor fracture toughness and defect sensitivity.Although the fracture toughness of SiC based ceramic can be improved by using liquid sintering method,the increase in toughness is typically accompanied by the drop in hardness using this method.Adding TiB₂ to SiC matrix can not only promote toughness via crack deflection but also combat the tradeoff of decreasing hardness.Till now,there is rarely report about using SPS technique to prepare SiC-TiB₂ composite ceramics.Meanwhile,the research on the evolution of intergranular phases and interfaces impacted by secondary phase has seldom been reported.Based on the above statements,our work prepared SiC-TiB₂ composite ceramics by SPS using YAG as sintering additive.Then we investigated the influence of sintering temperature,content of TiB₂ and the ratio of different SiC phase on the microstructure,intergranular phase interfaces and mechanical properties of SiC-TiB₂.The influence of sintering temperature on the composition and microstructure of SiC-TiB₂ was investigated by choosing 1600?,1700?,1750?as sintering temperature.With the increase of sintering temperature the Rel.density of ceramic increased and thus the bounding strength between grains improved.With the increase of sintering temperature,the fracture mode changed from intergranular fracture to the mixture of intergranular fracture and transgranular fracture.The flexural strength and hardness increased with the increase of sintering temperature.The maximum flexural strength of 753MPa and the maximum hardness of 23.19GPa were obtained at the sintering temperature of 1750?.The fracture toughness of samples increased at first and then decreased with the increase of temperature.The maximum fracture toughness of 8.84MPa·m^1/2 was obtained at the sintering temperature of 1700?.By choosing different contents?0wt.%,5wt.%,15wt.%,25wt.%?of TiB₂ added to SiC,the influence of TiB₂ content on the composition and microstructure of the samples was investigated.The results showed that the adding of TiB₂ led to lots of Si doped into intergranular phases,which changed the composition of intergranular phases,and thus changed the morphology of intergranular phases from crystalline phase to amorphous phase.Though the adding of TiB₂ had a negative effect on the densification of SiC-TiB₂,it reduced the content of O in the boundary of SiC/SiC and changed the morphology of intergranular phases from crystalline to amorphous phase which improved the bonding strength between grains and thus improved the flexural strength and fracture toughness.The flexural strength,fracture toughness and hardness of SiC-TiB₂ increased at first and then decreased with the increase of TiB₂.The maximum flexural strength of 662MPa,the maximum fracture toughness of 8.84MPa·m^1/2 and the maximum hardness of 22.36GPa were obtained in the sample with 15wt.%TiB₂.Via changing the polytype composition of SiC and subsequent heat treatment,the influence of polytype composition on the microstructure and mechanical properties of SiC-TiB₂ was investigated.The result showed that sintered at 1700?by SPS technique,the Rel.density,flexural strength and fracture toughness of samples decreased with the increase of the?-SiC ratio.After heat treatment at 2000?,part of?-SiC transformed into?-SiC which accelerated the anisotropic growth of grains.And thus the elongated?-SiC grains were obtained.The higher fracture toughness and flexural strength were obtained after heat treatment in the samples containing most of?-SiC,which transformed into elongated?-SiC after heat treatment.While the fracture toughness and flexural strength of samples containing most of?-SiC decreased after heat treatment due to the excessive growth of grains.