Fabrication And Machanical Properties Of ZrB₂-ZrC Composites

ZrB₂and its composites have been widely used in ultra-high temperatureceramic field due to its high melting point, high hardness, good high temperaturemechanical properties.While it has many shortcomings, such as low self-diffusioncoefficient, difficult to sintering densification, lower material strength andtoughness and high sintering temperature is demanding, all this limits its application.To solve these problems, we used eutectic components of ZrB₂-ZrC ceramicmaterials, high-energy ball milling broken powder, and two-step sintering method ofpressureless sintering and hot pressing to obtain dense composite. And three-pointbending, single edge notched beam methods and such as X-ray diffraction, scanningelectron microscopy and other analytical tools, were used to study the organizationalstructure and mechanical properties of composites.The results showed that mixing the powder with a certain amount of WCthrough ball milling, will increase the density of the material. During high energyball milling, the raw material powder particles was broken for the smaller particlesize, as well as more lattice defects, residual stress and so on, which increase thedriving force of sintering, shortening the diffusion path between the particles, andtherefore can increase the density of the material.Two step sintering has a great effect on the densification of the composites. Thetwo step sintered ZrB₂-ZrC composite that presureless sintered at2000℃reachthe highest mechanical properties. The density, hardness, bending strength andfracture toughness of the two step sintered composite were6.38g/cm3,17.6GPa,479MPa,6.9MPa·m^1/2, which has reached the property of the hot pressedcomposites. Strength of materials in hot pressing at1900℃is583MPa, but thehardness and density is lower than the pressureless sintering of the material.The best mechanical properties were attained in composite pressureless sinteringat2000℃，when the ZrB₂shows a club-shape morphology, which plays a importantrole in toughening the matrix.