B₄C基陶瓷复合材料的制备与研究

【作者】 张卫珂；

【导师】 张玉军； 龚红宇；

【作者基本信息】 山东大学 ， 材料学， 2006， 硕士

【摘要】 碳化硼（B₄C）具有低密度（ρ_v=2.52g/cm³）、高硬度（HV＞30GPa）、高模量、耐磨性好、抗氧化性、耐酸碱性强以及良好的中子吸收性能等特点，被国内外广泛用作防弹材料、防辐射材料、耐磨和自润滑材料、特种耐酸碱侵蚀材料、切割研磨工具以及原子反应堆控制和屏蔽材料等。由于碳化硼是共价键很强的陶瓷材料，共价键占90％以上，而且碳化硼的塑性差，晶界移动阻力很大，固态时表面张力很小，从而决定了碳化硼是一种极难烧结的陶瓷材料。常压下于2300℃烧结通常只能获得低于80％的相对密度，制品力学性能低，限制了其在许多领域的应用。 本文对B₄C进行活化烧结，添加的烧结助剂为Al₂O₃、Si、（Ti，W）C等，采用热压烧结工艺制备轻质碳化硼基复合陶瓷材料。对于添加Si的复合材料，通过原位生成的SiB₆提高B₄C材料的烧结性，并通过进一步加入SiC晶须制备了B₄C-SiC_w-SiB₆陶瓷复合材料。 本文利用显微压痕、三点弯曲、单边切口梁等实验方法测试了复合材料的力学性能，通过XRD、SEM等分析技术对B₄C-Al₂O₃、B₄C-（Ti，W）C、B₄C-SiB₆等系列复合材料的组织结构、相组成进行了分析，并对复合材料的补强增韧机制进行了分析探讨。研究结果表明： 1．Al₂O₃能有效地降低碳化硼陶瓷的烧结温度，并提高其弯曲强度；B₄C-Al₂O₃复合陶瓷材料的硬度随着Al₂O₃含量的增加而下降，特别是Al₂O₃含量超过10％时，硬度下降明显。分析认为，Al₂O₃降低碳化硼陶瓷的烧结温度的原因是由于AlB₁₂C₂的生成。AlB₁₂C₂作为液相的出现，促进了烧结体的相对密度是提高基体弯曲强度和断裂韧性的主要原因。 2．（Ti，W）C固溶体的加入，由于TiB₂、W₂B₅的生成，促进了B₄C-（Ti，W）C复合材料的致密化烧结，提高了复合陶瓷的断裂韧性，断裂韧性达到5.8MPa·m^1／2，远高于单一碳化硼陶瓷。 3．Si的加入可以降低碳化硼基复合陶瓷材料的烧结温度。采用原位生成SiB₆的方法对促进B₄C陶瓷材料进的烧结，提高了B₄C基复合陶瓷材料的性能。对于Si含量10wt％的B₄C陶瓷复合材料，粉料在900～1400℃下8h预烧处理后，其烧结体弯曲强度和断裂韧性分别达到447.2MPa和4.62MPa·m^1／2。更多还原

【Abstract】 Boron carbide （B₄C） ceramics has been recognized as one of the important and promising engineering ceramics due to its is widely used in wearable materials, light bombproof armor and space flights etc because of its excellent physical and chemical properties, for instance, super-hardness （HV>30MPa）, high melting point （2450℃） and low density （2.52g/cm³）. And now it is widely used in bulletproof materials, radiation protection materials, lubricate materials, wearable materials, sharpener materials and shield materials etc. However, because of the strong covalent bond , Boron carbide is difficult to be sintered. When Boron carbide is sintered at 2300℃ in normal atmosphere, the density only can get to 80%, furthermore the mechanical properties are not perfect, so , it cannot satisfied the engineering demands.In this paper, reactive hot-pressing （RHP） is used to prepare light-duty B₄C matrix composites ceramics at a relatively lower temperature by adding activation additives （Al₂O₃、 Si、 （Ti,W）C） into B₄C matrix. B₄C is reinforced and flexed by the generation of SiB₆ in suit. To improve the fracture toughness of the B₄C composites by adding whiskers.XRD、 SEM technologies are used to detect the microstructure and the phase. Mechanical properties are measured by micro-indentation, three-point bending methods. The analysis shows: Al₂O₃ can be used to low the sinter temperature, and it can improve the flexural strength. When the weight of Al₂O₃ under 10%, the hardness of B₄C composite ceramics is hardly influenced. The adding of （Ti,W）C can increase the fracture toughness of B₄C composite ceramics due to the forming of TiB₂ and W₂B₅, which can create the mismatch of heat expansions. The adding of Si can low the sinter temperature obviously, at the same time, the mechanical properties of B₄C are increased because of the generation of SiB₆ in suit.The cracking mode of B₄C matrix composites ceramics is the combination of inter-granular fracture and trans-granular fracture. And the former is mainly. The reinforced-toughened factors include fine-grain, whiskers, plate-like structure, special scattering phases and residual thermal stress.更多还原