Fabrication And Properties Analysis Of ZrB₂-Based Ceramic Composites

Because of its strong covalent and ionic bonding, ZrB2has a high melting temperature, high hardness and wear resistance. The excellent physical and chemical properties make ZrB2the most promising structural materials in harsh service environment. But as a result of its low self-diffusion coefficient, to achieve fully dense monolithic ZrB2ceramics is very difficult. In this study ZrSi2added as a sintering aid to acquire high relative density ZrB2at low temperature. For the inherent brittleness of ceramic materials, WC particles and chopped carbon fiber are used for toughening in this thesis. In the fabrication of ZrB2ceramic matrix composite material, hot-pressing sintering process has been used. The sintering temperature is1400℃～1600℃, the sintering pressure is30MPa. The phases of the composites are examined by X-ray diffraction (XRD) and Scanning Electron Microscope (SEM). In this paper, the two main toughening mechanism are discussed:By addition to different volume fraction of ZrSi2, high relative density ZrB2ceramic matrix composites were fabricated. The volume fraction of15%,20%and25%ZrSi2as a sintering aid is selected and the volume fraction of5%WC as particulate reinforcement is selected in this paper. After hot-pressing process, the relative densititation of the composites are all above99%. By three-point bending experiments and unilateral opening beam test. The flexural strength up to634MPa and fracture toughness up to6.87MPa m1/2, its high fracture toughness is mainly due to the pullout of the rodlike ZrB2grains. Phase by XRD and SEM analysis showed that the ZrB2-ZrSi2-WC composites formed two substitutional solid solution.ZrB2-20vol%ZrSi2-Cf with the volume of content of short carbon fiber about5%、10%、20%and30%, were fabricated and especially it has a considerable better mechanical properties and microstructure when the volume of the fiber content is about20%. At the same time, the difference between untreated and treated fibers under1500℃were analyzed. The fiber surface is covered with a protective layer of silicate after being heated, therefore it protects the fibers form the erosion by the matrix. The fracture toughness of ZrB2-20vol%ZrSi2-Cf can reach6.3MPa m1/2, while its bending strength is relative low.