The Research Of Stengthening, Toughening And High-Temperature Properties Of MoSi₂ Ceramic Matrix Composite

MoSi₂ nano-precursor powder was synthesized by mechanical alloying (MA), and CNT was dispersed with ultrasonic. The MoSi₂ and CNT were mixed by wet-milling and then made into MoSi₂ matrix composite using hot-pressing. The mechanism of MA and dispersing of CNT, the optimizing of hot-pressing, the mechanical properties and the microstructure of the composite were studied by X-ray diffraction (XRD), optical microscope (OM), scanning electron microscope (SEM), energy dispersive spectrum (EDS) and mechanical analysis.The research results show that nanosize MoSi₂ with little impurity is synthesized though milling at a rotate speed of 510r/min for 24h using Mo and Si powder mixed by an atom ratio of 1:2, adding alcohol as process monitoring agent protected by an inert argon atmosphere. The nano-precursor powder is a basis for decreasing sintering temperature and optimizing the procedure during fabrication of the CNT/MoSi₂ composite.CNT is dispersed in alcohol solvents incorporated with C₁₂H₂₅SO₃Na by ultrasonic agitation to decrease its conglobation.The optimal fabrication process of CNT/MoSi₂ composite is: heating-up powder to 800℃at the speed of 15℃/min, and insulating for 1 h, compressing powder slowly at 700℃, continuing heating-up powder to 1400℃at the speed of 20℃/min and insulating and maintaining pressure for 45 min and then furnace cooling to room-temperature. After this process, CNT/MoSi₂ composite with relative density above 90% is obtained.The material without CNT is composed of MoSi₂ and a little of Mo5Si3. In the composite, a small amount of SiC appears and the amount of Mo₅Si₃ is increased. The Mo₅Si₃ has fine grain sizes and is evenly distributed, which will be propitious to the high-temperature properties of the composite.CNT improves the strength and toughness of the composites. The bending strength of the composites with the CNT addition of 2.5wt%, compared with the monolithic MoSi₂, is enhanced 72%, and the fracture toughness of composite added with 1wt% CNT becomes 1.43 times of the monolithic MoSi₂.The strength of CNT/MoSi₂ composites does not decrease below 1000℃.