【作者】 包建勋；

【导师】 马南钢；

【作者基本信息】 华中科技大学 ， 材料学， 2009， 硕士

【摘要】 1800℃下无压烧结骨架预置体,在真空中或压力为一个大气压的氩气气氛中对骨架熔渗金属Al,可以制备出密度小于2.6g/cm3的复合材料,致密度均超过96%,相对于1atm高纯氩气气氛,真空下铝的熔渗效果更佳。通过调整颗粒级配能够控制复合材料中各物质相的含量从而控制力学性能。有机添加剂采用PVB作为粘结剂,PEG2000为增塑剂以及无水乙醇为溶剂,通过轧膜成型制备表面无缺陷的B₄C大规模陶瓷薄片。实验表明,选择粘结剂时避免其因为氢键或缩聚交联是关键。B₄C/Al复合材料的抗弯强度主要决定于陶瓷骨架预置体的烧结强度,而陶瓷骨架的强度主要由烧结质量控制。复合材料的弹性模量受烧结质量影响较小,主要与物质相含量有关。实验显示,该工艺下制备的复合材料的断裂韧性随着抗弯强度水平的提高而提高。同时也由于复合材料具有的宏观均匀,微观非均匀的结构,给传统的硬度测量带来较大的偏差,矛盾集中在要求硬度测量时尽可能用较低载荷,同时也要求硬度测量时试样和压头具有大的面积接触从而保证选取点的代表性。B₄C/Al复合材料裂纹的起源为内部气孔,断裂过程受裂纹的扩展控制。随着载荷的增加,裂纹的扩展行为经历四个阶段:裂纹在脆性陶瓷相中的快速扩展;裂纹尖端接触金属增韧相钝化;在相界面裂纹偏转或者沿扩展面绕开金属增韧相向后方扩展;形成韧性相桥架,材料失效但保留了韧性相的残余强度。在后三个阶段,增韧相起提高裂纹扩展阻力的作用。更多还原

【Abstract】 Boron carbide skeletons with tri-dimension co-continuous opening pores were sintered by pressureless sintering methods at 1800℃, then was infiltrated by Al in vacuum environment or in Argon atmosphere. A composite with co-continuous phases of ceramics and metal were successfully fabricated, which was almost fully condensed to the density higher than 96% with mass density lower than 2.6g/cm3.Compared with the specimens infiltrated with Al in Argon atmosphere under 1 bar, the quality of the others prepared by infiltration under vacuum condition turns out to be better. By adjusting the sizes distribution of boron carbide particles, the content of each phase of the final products could be under controlled, through which the mechanical properties of those composites could be regulated.By choosing proper organic additive, thin sheet of B₄C porous ceramics with large area could be obtained with the method of rolling forming process. PVB has been proved by experiment be an effectual binder as well as PEG2000 as dispersant and plasticizer. With these two kinds of organic additives, the flexibility and the surface quality of green body of the sheets are guaranteed. One principle to pick binders for boron carbide rolling forming is to avoid the polycondensation between the -OH from boric acid and that from the polymer, which causes cross-linked among polymer chains.The flexural strength of B₄C/Al composite strongly depends on the strength of boron carbide skeleton, which is determined by sintering quality. The sintering quality has little influence on elastic modulus of those composites. The values of the elastic modulus of those composites are related to the content of material phases. Experiments show that by the preparation technique, the values of fracture toughness of the composites go on higher level while bending strength is higher; which could not gain rational explanation from the classical Griffith Theory. Since the composite has a macro-homogeneous, micro-inhomogeneous structure, some large deviation would be brought about from the traditional hardness measurement. Accurate hardness measurement requires low indenting load, and indenting area being large enough so that we can make sure the statistically representative of the point tested.The fracture behavior of B₄C/Al composite is controlled by crack propagation. Crack propagation will experience four stages: rapid crack propagating in brittle ceramic phase; pinning appears when crack tips contact metal toughening phase; crack deflecting at phase interface or propagating backward along the extended surface; toughening phase bridging frame, materials fail but retain the residual strength of the toughening phase. At the last three phases, the resistant of crack propagation comes from toughening phase.更多还原