Synthesis And Properties Of Ti₃SiC₂/SiC Composites

In this paper, Ti₃SiC₂/SiC multiphase ceramics containing different contents of SiC are fabricated with TiH₂, SiC and graphite powders by in situ synthesis under hot isostatic pressing (HIP) and transient plastic phase processing(TPPP) to provide new ideal for the application of Ti₃SiC₂. Phase, grain size, grain appearance and fracture mechanism of Ti₃SiC₂/SiC composites are investigated by X-ray diffraction, optical microscope. The performances of Ti₃SiC₂/SiC composites by in situ synthesis under hot isostatic pressing (HIP) was studied via the test results on their densities, micro-hardness, fracture toughness, properties of friction and wear, and the resistance of oxidation. The research indicates that Ti₃SiC₂/SiC composites has good overall performance for high temperature structural material.Ti₃SiC₂/SiC composite samples consisting of 3,4,5,7mol SiC are full dense and the relative densities are beyond 98.5%. Ti₃SiC₂/SiC composites under HIP consisting of 10 mol SiC, In this way, Ti₃SiC₂ can not form successive net shape and be fully compact. So the relative density of sample consisting 10mol SiC only reaches 90.4%.The XRD results indicate that the major phases of Ti₃SiC₂/SiC composites are Ti₃SiC₂ and SiC, and a few TiC phases. Basically, it accords with the results designed. The results measured for micro-hardness and fracture toughness have been demonstrated that the micro-hardness of composites ceramics increases along with contents of SiC and maximum is 14.1GPa. Comparably, the fracture toughness decreases with increasing SiC and maximum is 7.24 MPam^1/2. The conductivity of composites decreases with increasing of SiC. It is identical with result of theoretical calculation.The tests of friction and wear properties of Ti₃SiC₂/SiC composites werecarried out using block-on-ring type testes to comparably research the friction and wear behaviors in different pairs, loads, and lubrication conditions. The friction coefficient of TljSiC^SiC composites is relatively low and wear rate is quite high during dry sliding, On the other hand, low friction coefficient and wear rate during lubricated sliding. The wear mechanism is considerably caused by micro-fracture.The oxidation behaviors of TisSiC^SiC composites with different temperatures and atmospheres have been discussed. Furthermore, the oxidation mechanism of TiaSiC^SiC composites was analyzed with in situ observation at high temperature and XRD. It is concluded that the high temperature oxidation dynamics curve of multiphase ceramics obeyed a parabolic law from 800 "C to 1400 °C .While temperature rising, the oxidation parabolic rate constantly increased. In the different atmospheres, oxidation could be related with oxide pressure. In the same case, oxidation mass gain rises with increasing the oxide pressure. Comparing the oxidation behaviors of TiaSiC^SiC composites with different SiC at 1200 °C, the growth of the oxide scale on TbSiC^SiC composites per area decreases with increasing in the contents of SiC. It is demonstrated that the oxidation resistance property of all Ti3SiC2/SiC composites is better than that of pure Ti3SiC2. The calculated activation energies of 7SiC and 3SiC composites are 2O8.129KJ.mor1 and 219.5 KJ.mol"1 respectively, and less than activation energy of pure Ti3SiC2. The oxide scale composed of TiO2, SiO2 grains and amorphous SiO2 can hinder the diffusion process, and results in good oxidation resistance.