| Zirconium diboride (ZrB2) is one of the best ultra-high temperature ceramics (UHTCs) with a combination of many unique advantages such as high melting point, high strength, high hardness, good thermal and electric conductivity and corrosion resistance ability. As a new material, Al3BC3was chosed as the sintering additive of SiC to improve the mechanical properties of SiC ceramics, because of its excellent characteristics of high temperature, high hardness, low density and high modulus.In this paper, ZrB2-Al3BC3and ZrB2-SiC-Al3BC3ceramic composites were prepared by hot pressing sintering and spark plasma sintering, respectively. The phase fraction and microstructure of materials were analyzed with X-ray diffraction (XRD) and scan electron microscopy (SEM). Density, relative density, hardness, bending strength and fracture toughness of materials were characterised; Thermal shock resistance and resistance to oxidation were characterized and analyzed of the two materials, spectively. The mainly results were shown as followes:(1) ZrB2-Al3BC3material was fabricated by reactive hot-pressing at1900℃under a20MPa uniaxed load in a flow Ar atmosphere for lh, with the ZrB2and Al-B4C-C material. Fully densified ZrB2-Al3BC3ceramic composite material was prepared successfully. The bending strength and fracture toughness of ZrB2-Al3BC3material decreased firstly and then increased with the increase of Al3BC3content. The bending strength reached a maximum of304.11MPa when the content of Al3BC3was15wt.%; While the Al3BC3content was5wt.%, the fracture toughness of the material reached the maximum of4.4MPam1/2.(2) ZrB2-SiC-Al3BC3ceramic composite material was prepared by adding Al-B4C-C sintering additives to ZrB2-SiC matrix, using SPS sintering method at1600℃,1700℃and1800℃respectively under a40MPa uniaxed load for5min. Fully densified ZrB2-SiC-Al3BC3ceramic composite material was prepared at low temperature successfully for adding Al3BC3and small initial particle size. Compared with the traditional ZrB2-SiC material, mechanical properties of material, especially the flexural strength and fracture toughness, were improved obviously with the addition of Al3BC3. The two performance of ZrB2-Al3BC3material increases with the increase of the sintering temperature. While the sintering temperature is1800℃, the bending strength and fracture toughness reached the maximum value:748.27MPa and6.15MPam1/2, respectively.(3) Thermal shock resistance of ZrB2-Al3BC3materials were tested at different temperature difference. Thermal shock resistance of the ZrB2-15wt.%Al3BC3material is the best for the critical temperature difference reached396℃. The critical temperature difference of ZSABC3material, sintered at1800at, is592℃, which belongs to the excellent level. The thermal shock resistance of materials was effected greatly by the addition of Al3BC3and formation of platelike grains.(4) ZrB2-Al3BC3shows great antioxidant at or below1100℃. Weight gain per unit area of ZrB2-10wt.%Al3BC3sample is3.04mg/cm2at1100℃for45min, which is the best one. Weight gain per unit area of ZrB2-SiC-Al3BC3material is only2.43-3.75mg/cm2at1300℃for45min. The oxidation mechanism of ZrB2-SiC-Al3BC3material was decribed as the formation of SiO2, Al2O3and B2O3on the surface of the sample and material can be protected with a glass phase formed by the three.Formed protective layer was broken and dense holes formed on it for the violent gasification of the internal and surface B2O3when the temperature continued to rise, then the oxidation resistance of the materials decreased with it.(5) The flexural strength of ZrB2-15wt.%Al3BC3material, with a high temperature oxidation at1000℃, enhanced to361.47MPa, which is about20%. Bending strength of ZrB2-SiC-Al3BC3increased to908.67MPa, about35%higher than it at room temperature, after a high temperature oxidation at1300℃. A great change was observed at internal structure and surface oxidation state of material after high temperature oxidation, and the bending strength of the material was influenced remarkablly by the both of two. |
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