【作者】 王生学；

【导师】 陈朝辉；

【作者基本信息】 国防科学技术大学 ， 材料科学与工程， 2011， 硕士

【摘要】 C/SiC复合材料是一种新型高温热结构材料,在航空航天和军事领域具有潜在的应用背景,但其耐高温、抗氧化性能不足,长期使用温度不超过1650℃,1700℃以上性能显著下降。为了解决C/SiC复合材料在耐高温、抗氧化性能的缺陷,本文采用先驱体转化法（PIP）,将ZrO₂引入SiC基体中,制备了ZrO₂改性的C/SiC复合材料,系统研究了ZrO₂的引入方式、ZrO₂引入后基体陶瓷的氧化和烧蚀机理以及ZrO₂的引入导致复合材料性能的变化。首先对作为ZrO₂先驱体的含锆化合物进行筛选,候选材料有含锆有机物:乙酰丙酮锆（Zr（AcAc）4）、正丁醇锆（Zr（OBu）4）、正丙醇锆（Zr（OPr）4）和含锆无机物:八水合氧氯化锆（ZrOCl2?8H2O）。研究发现,三种有机锆源均可溶于PCS的DVB溶液,采用Zr（OBu）4为有机锆源制备的浸渍液具有最佳的工艺性能和陶瓷产率,最佳配比为PCS:DVB:Zr（OBu）4=2:1:2,陶瓷产率为43.93%;ZrOCl2?8H2O在甲醇中溶解度较好,并且与SiC陶瓷及C/SiC复合材料具有较好的浸润性,可以用于制备浸渍液,陶瓷产率为12.3%。为了研究ZrO₂的引入对基体性能的影响,制备了ZrO₂改性SiC本体陶瓷。结果发现,在本体陶瓷中,ZrO₂以细碎的颗粒状存在于块状SiC之间;随着ZrO₂含量的提高,材料的孔隙率也提高,当ZrO₂含量为29wt%时,孔隙率为23.6%,密度2.16g/cm3,加压浸渍可以降低本体陶瓷的孔隙率,采用加压浸渍工艺制备的本体陶瓷ZrO₂含量为14.3wt%,而孔隙率仅为7.89%,密度达2.31g/cm3;随着ZrO₂含量的提高,本体陶瓷在1700℃下的氧化失重增大,力学性能保留率下降,与ZrO₂含量为7wt%的本体陶瓷相比,含量29wt%的本体陶瓷在1700℃的氧化失重由1.23%升至15.58%,抗弯强度保留率由59.16%降至36.84%;ZrO₂改性SiC本体陶瓷的氧化行为分为三个阶段:第一阶段,在800¹500℃,SiC的惰性氧化占主导地位,主要氧化生成SiO₂,第二阶段,1500¹600℃,SiC的活性氧化逐渐占主导地位,SiO开始生成,第三阶段,1600℃以上,SiC活性氧化占主导地位,ZrO₂的碳热还原反应开始发生,并且PCS裂解SiC进一步分解放出气体,导致SiO₂玻璃相阻氧层破裂,材料内部暴露在空气中发生进一步氧化;ZrO₂改性SiC本体陶瓷的烧蚀率随着ZrO₂含量的提高而降低,ZrO₂含量从7wt%升至29wt%,本体陶瓷的质量烧蚀率由0.0367g/s降至0.0195g/s,ZrO₂含量为7wt%的材料烧蚀后裂开,29wt%的材料线烧蚀率为0.0361mm/s,烧蚀后本体陶瓷从中心至边缘ZrO₂含量降低,ZrO₂集中在烧蚀中心凹坑处,边缘部分集中了大量的SiO₂。在基体研究的基础上,制备了ZrO₂改性的C/ SiC复合材料,对其结构和性能进行表征,并对其氧化和烧蚀机理进行分析。研究发现,采用前几个周期浸渍PCS/Xylene的方式可以有效保护C纤维,保护后材料的抗弯强度明显提高,ZrO₂含量为25wt%的复合材料的抗弯强度为216MPa,未经保护的复合材料仅为103MPa;ZrO₂改性的C/SiC复合材料的抗弯强度主要与孔隙率有关,ZrO₂含量较多会导致孔隙率较高,但加压浸渍可以弥补这一缺点,加压浸渍制备的复合材料ZrO₂含量为9.0wt%,孔隙率仅为4.78%,抗弯强度达292MPa;1700℃氧化条件下,ZrO₂的天然氧化性开始显现出优势,使材料整体的抗氧化性提高,ZrO₂含量61wt%、25wt%和16wt%的材料1700℃下失重率分别为29.98%、34.71%、35.07%;ZrO₂含量为61wt%的材料质量烧蚀率和线烧蚀率分别为0.0161g/s和0.0185mm/s,比未引入ZrO₂的C/SiC复合材料（质量烧蚀率和线烧蚀率分别为0.0223g/s和0.0602mm/s）有较大幅度的降低。更多还原

【Abstract】 Carbon fibre reinforced silicon carbide（C/SiC） composites is a new type of high temperature structural material with the potential application in the aeronautic, astronautic and military fields.However,C/SiC cannot be long-term utilized above 1650℃and properties are obviously declined above 1700℃due to the shortage of high temperature endurance and oxidation resistance. In this dissertation, ZrO₂ modified C/SiC composites were designed and fabricated by precursor infiltration pyrolysis （PIP） method. Systematic investigation were studied of the induction route of ZrO₂, oxidation and ablation behavior of matrix modified by ZrO₂,and the effect of content of ZrO₂ on the properties of C/SiC composites.Firstly, this paper focused on the choice of precursor on candidation of zirconium-2,4-pentanedionate（Zr（AcAc）4）, zirconium n-butoxide（Zr（OBu）4） and zirconium n-propoxide（Zr（OPr）4） as organical precursor, ZrOCl2?8H2O as inorganical precursor. The result revealed that the organical precursor can dissolve into PCS and divinylbenzene（DVB） mixture, and Zr（OBu）4 is the most suitable precursor with the proportion of PCS:DVB:Zr（OBu）4=2:1:2 of which the yield is 43.93%. ZrOCl2?8H2O can be utilized as precursor due to high solubility in methanol and good infiltration in SiC ceramics and C/SiC composites and the yield is 12.3%.For the purpose of investigating the effect of ZrO₂ additional to properties of matrix, ZrO₂ modified SiC ceramics were prepared. ZrO₂ existed in the form of thin grains among SiC blocks.With increasing content of ZrO₂, the porosity increased consistently, the porosity of ceremics with 29wt% ZrO₂ was 23.6% and density was 2.16g/cm3. Infiltration with pressure can decrease the porosity. Ceramics prepared by this method of which ZrO₂ content was 14.3wt% had porosity 23.6%, and density 2.31g/cm3. After oxidation at 1700℃, with the content of ZrO₂ increasing, weight loss increased and retention of flexural strength decreased. Compared to ceremics with 7wt% ZrO₂, weight retention of ceremics with 29wt% ZrO₂ decreased from 59.16% to 36.84%. Oxidation behavior of ZrO₂ modified SiCceramics may be divided into three steps according to the temperature gradient. Firstly, oxidation of free C and passive oxidation of SiC forming SiO₂ happened at 800℃to 1500℃. Secondly, according to the temperature rising and pressure of O₂ decreasing, active oxidation of SiC gradually became dominant which formed SiO gas at 1500℃to 1600℃. Then, above 1600℃, carbo-thermal reaction began and pyrolysis of PCS continued with gas forming, which caused the protective SiO₂ destroyed and the inner region of the ceramics was oxided. The ablation rate decreased with content of ZrO₂. when ZrO₂ increased from 7wt% to 29wt%, the mass loss rate changed from 0.0367g/s to 0.0195g/s, and the linear recession rate changed from cracked to 0361mm/s. After ablation, proportion of ZrO₂ decreased from the ablation center to edge, ZrO₂ existed mostly at the ablation center and SiO₂ at the edge.ZrO₂ modified C/SiC composites were fabricated on base of the ceramics, and the structure and properties were investigated, the mechanisms of oxidation and ablation were also researched. The result showed that, C fibers were efficiently protected by ways of infiltrating PCS/Xylene at the former cycles.Flexual strength was obviously improved, flexural strength of composites with 25wt% ZrO₂ was 216MPa and the one without protection was only 103MPa. Infiltration with pressure can make up this limitation. Composites fabricated with pressure had ZrO₂ content 9.0wt%, porosity 4.78% and flexural strength 292MPa. The intrinsically resistant to oxidation of ZrO₂ emerged at 1700℃, which improved the oxidation resistance of whole material. Composites with ZrO₂ 61wt%,25wt% and 16wt% had weight loss of 29.98%, 34.71% and 35.07%. Compared to C/SiC composites（0.0223g/s and 0.0602mm/s）, the mass loss rate and linear recession rate of 61wt% ZrO₂ composites was 0.0161g/s and 0.0185mm/s.更多还原