碳短纤维对ZrB_2-SiC基超高温陶瓷力学性能的影响

Effects of Short Carbon Fiber on Mechanical Properties of ZrB_2-SiC Ultra-high Temperature Ceramics

ZrB2-SiC基材料具有高熔点,高热导率,高电导率和良好的化学稳定性,可以在高超声速的极端条件下工作。但是这种材料的主要问题是低的断裂韧性,为了改善这一性能,将碳短纤维加入到ZrB2-20%(体积分数)SiC中热压烧结,得到了断裂韧性明显提高的试样,从2.0MPa.m1/2提高到6.56MPa.m1/2,同时弯曲强度略有降低,从502MPa降至445MPa,弹性模量也有所降低,从414GPa降至322GPa。为了深入理解这种变化,建立了模型来计算纤维造成的影响,计算结果与实验结果比较接近,证明对于本实验的材料体系,用该模型来解释是合理的。

Zirconium diboride-silicon carbide based ceramics are attractive for application in aircraft propulsion systems and thermal protection system for hypersonic vehicle because of their high melting point, high thermal and electrical conductivity and good chemical stability. However, the major problems associated with ZrB2/SiC are lack of damage tolerance and insufficient strength as structure components. ZrB2-20%（volume fraction） SiC ceramics with the additional short carbon fiber was developed to promote graceful failure using hot pressing technique. The results show that the introduction of short carbon fiber into the ZrB2-20%SiC matrix results in an apparent increase in fracture toughness from 2.0MPa · m1/2 to 6.56MPa · m1/2 and not evidently change in flexural strength from 502MPa to 445MPa and elastic modulus from 414GPa to 322GPa. Meanwhile the influence of short carbon fiber on the strength, and modulus is analyzed and estimated using a modified role-of-mixture formulation and that on the toughness is also calculated based on the toughening mechanisms of crack bridging, fiber pullout and crack deflection. The calculated results of the strength, elastic modulus and fracture toughness of the composite agree well with the experimental results.