【作者】 艾云龙；

【导师】 王珉； 左敦稳；

【作者基本信息】 南京航空航天大学 ， 机械制造及其自动化， 2008， 博士

【摘要】 MoSi2是一种金属间化合物,它具有较高的熔点、较低的密度和良好的高温抗氧化性,作为高温结构材料和室温摩擦材料在航空和汽车领域有着广泛的应用前景。但MoSi2室温脆性高而高温强度低,成为其实用化的主要障碍。本文为了提高MoSi2的综合性能,基于纳米改性技术,提出了采用纳米SiC/ZrO2颗粒、SiC晶须/ZrO2纳米颗粒协同复合MoSi2陶瓷的构想,从制备工艺、组织结构、力学性能等方面开展深入系统的探讨,为MoSi2基复合材料在结构材料中的应用奠定基础。本文完成的主要工作和取得的成果如下:1.利用多相悬浮液混合法制备了SiC/ZrO2-MoSi2复合粉体,发现以聚乙二醇为分散剂、水为分散介质,并利用超声振荡分散以及SiC晶须通过调节乙醇悬浮液的pH值,可获得各相分布均匀的SiC(W)/ZrO2-MoSi2复合粉。2.利用热压烧结制备了SiC/ZrO2 -MoSi2纳米复相陶瓷,通过对复相陶瓷的相组成与显微结构和力学性能的分析,发现SiC/ ZrO2协同作用综合机制提高复相陶瓷抗弯强度、断裂韧度以及细化晶粒作用明显,20%SiC(p)+10%ZrO2+MoSi2的抗弯强度是MoSi2的3.8倍,断裂韧度为2.4倍;15%SiC(w)+15%ZrO2+MoSi2的抗弯强度是MoSi2的2.6倍,断裂韧度为2.5倍。3.首次利用密栅云纹干涉法测试分析了纳米复相陶瓷高温断裂韧度,发现SiC/ZrO2协同作用提高复相陶瓷高温断裂韧度,纳米ZrO2颗粒高温增韧效果优于纳米SiC颗粒,纳米SiC颗粒高温增韧效果优于SiC晶须。4.利用压痕-急冷法研究了SiC/ZrO2 -MoSi2纳米复相陶瓷在100℃～600℃温差范围内的抗热震性能,发现纳米SiC颗粒或晶须与纳米ZrO2颗粒协同复合MoSi2改变了陶瓷裂纹扩展路径和形态,提高抗热震性能;纳米SiC颗粒提高MoSi2抗热震性能效果优于SiC晶须。探讨了SiC/ZrO2 -MoSi2纳米复相陶瓷“粉化”现象、抗氧化性能以及表面膜形成机制,发现复相陶瓷“粉化”现象减弱或没有,表面玻璃膜易形成,SiC/ZrO2协同作用有利于高、低温抗氧化能力的提高。5.通过室温磨损试验,测试分析了SiC/ZrO2-MoSi2纳米复相陶瓷的磨损特性,发现SiC/ZrO2协同作用能明显改善MoSi2陶瓷的耐磨性,纳米ZrO2颗粒的加入使复相陶瓷粘着磨损比例增大,纳米SiC颗粒的加入使复相陶瓷的磨粒磨损比例增大;纳米SiC/ZrO2颗粒与SiC晶须/ZrO2纳米颗粒协同作用相比,前者复相陶瓷磨粒磨损特征更明显。6.首次利用X射线衍射法研究了SiC/ZrO2-MoSi2纳米复相陶瓷微观应变,分析了SiC/ZrO2协同作用与MoSi2基体的位错关系,探讨了复相协同作用增韧补强MoSi2的机制,发现复相陶瓷断裂过程中ZrO2微观应变下降,部分转变为应力诱导ZrO2发生相变以及形成微裂纹,纳米SiC颗粒弥散分布在复相陶瓷中,难以缓解周边基体对其包围所产生或传递的应力,微观应变较大;ZrO2依靠自身相变的体积效应向基体泵入位错,晶内型SiC和ZrO2粒子对复相陶瓷位错的钉扎作用明显,SiC晶须阻碍位错运动,使位错缠结、交割,形成位错网结,另外,第二相粒子周围出现孪晶以及SiC晶须引起层错;复相陶瓷的韧化效应是ZrO2粒子的相变韧化及微裂纹形成、SiC晶须或SiC和ZrO2粒子的裂纹偏转和桥联、细化晶粒以及复合材料“内晶型”结构等机制的综合作用;复相陶瓷的强化机制主要为细晶强化和弥散强化。更多还原

【Abstract】 MoSi2 intermetallics possess an unusual combination of the properties such as low density, high melting temperature and good oxidation resistance at high temperatures. These unusual combinations of the properties render them promising applications for friction materials at room temperature and high temperature structural materials widely used in the fields of aviation and auto. However, the high room-temperature brittleness and poor high-temperature strength are the main obstacles of its application. Based on nanoparticles modification technlolgy, the preparation of MoSi2 matrix nanocomosites was proposed compostied with SiC/ZrO2 nanoparticles or SiC whisker/ZrO2 nanoparticles in order to improve the combination properties of MoSi2 ceramics. Furthermore, systemic investigation were based on the preparation process, microstructure and mechanical properties, which provide foundation for the application of MoSi2 matrix nanocomosites as sturcture materials.The main work done and the results obtained in this thesis are as follows:1. SiC/ZrO2 -MoSi2 composite powders were prepared by multi-phase suspending solution mixture. In this experiment, polyethylene glycol acted as dispersant agent, water acted as dispersive medium, and dispersed the SiC whisker in ultrasonic bath and adjusted pH in the ethanol suspending solution. According to above mentioned method, all phases complete mixed SiC(w)/ZrO2-MoSi2 composites powders were obtained.2. SiC/ZrO2-MoSi2 ceramic nanocomposites were prepared by hot pressed sintering. The synergic effect of SiC/ZrO2 to improve bending strength, fracture toughness and grain refining were observed by microstructure observation and mechanical property analysis. Compared to MoSi2 ceramics, for 20%SiC(p) +10%ZrO2+MoSi2, the bending strength increased by 3.8 times, the fracture toughness improved by 2.4 times; Furthermore, for 15% SiC(w)+15%ZrO2+MoSi2, the bending strength increased by 2.6 times, the fracture toughness improved by 2.5 times.3. The high-temperature fracture toughness of ceramic nanocomposites were analyzed used Moiréinterferometry for the first time. It was found the SiC/ZrO2 synergism enhanced the high-temperature fracture toughness of ceramic nanocomposites. The effect of ZrO2 particle on high-temperature toughening were better than that of SiC particle, and the effect of SiC particle on high temperature toughening were better than that of SiC whisker.4. The heat-shocking resistance of SiC/ZrO2-MoSi2 ceramic nanocomposites were studied using indentation-quick cooling method in the temperature range from 100℃to 600℃. The results showed that the SiC particle or whisker combined with ZrO2 nanoparticles changed the expand path and shape of the cracks in MoSi2 ceramics, which enhanced the heat-shocking resistance. The effect of SiC particle on improving heat-shocking resistance of MoSi2 were better than that of SiC whisker. The“pesting”phenomena, oxidation resitance as well as the forming mechanism of the surface film of SiC/ZrO2-MoSi2 nanocomposites were discussed. The results showed that the“pesting”phenomenon decreased or did not exist, the amorphous film was easy to form on the surface, and the SiC/ZrO2 synergism was advantageous to improve the high and low temperature oxidation resistance.5. The wear characteristic of SiC/ZrO2-MoSi2 nanocomposites were analyzed through the wear test on room temperature. The results showed that the SiC/ZrO2 synergism could improve the wear resistance of MoSi2 ceramics obviously. The addition of ZrO2 nanoparticles caused the proportion of adhesive wear increase, and the addition of SiC nanoparticles caused the proportion of abrasive wear increase. Abrasive wear characteristic of SiC/ZrO2 nanoparticles composited MoSi2 was more obvious than that of SiC whisker/ZrO2 nanoparticles composited MoSi2.6. The microstrain of SiC/ZrO2-MoSi2 nanocomposites were investigated using X ray diffraction firstly. The dislocation relation between SiC/ZrO2 synergism and MoSi2 matrix were analyzed. The mechanism of toughening and strenghening were discussed as well. It was discovered that the microstrain of ZrO2 decreased in the fracture process, which caused by part of stress inducing ZrO2 transform to form microcrack. SiC nanoparticles distributed in the composite ceramics induced high microstrain as the result of difficulty alleviating the stress that substrate around them bring or pass. ZrO2 produced dislocation in the substrate depending on volume effect caused by its own phase transitions. The pining effect of intracrystalline type SiC and ZrO2 particles on the dislocation in the composite ceramics was obvious, and the SiC whisker block dislocation movement which caused the dislocation tangle, intersect and formed the dislocation network knot. Moreover, the twin crystals appeared around the second particles as well as the SiC whisker caused stacking faults. The toughening meachanism of composites concludes the phase transitions toughening and microcrack forming of ZrO2 particles, the crack deflection and bridge union of SiC whisker or SiC and ZrO2 particles, the grains refined as well as“intracrystalline type”structure in the composites and so on. The strenghening meachanism of composites was mainly for the fine-grain strengthening and dispersion strengthening.更多还原