【作者】 周立娟；

【导师】 杜善义；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2009， 博士

【摘要】 导电陶瓷是集金属电学性质和陶瓷结构特性于一体的高性能功能材料,具有一般金属所不能比拟的物理化学性质。本文以Al+N2 AlN反应为基础,添加一定量的TiB₂或TiN导电相,在100MPa高压氮气下,采用燃烧合成工艺制备了AlN基复相导电陶瓷。通过调节导电相、绝缘相的比例,获得不同导电率的高温导电陶瓷。由于体系各组分均具有很高的熔点,因而该体系导电陶瓷具有优良的高温性能,同时具有极好的耐腐蚀和耐磨损特性。本文首先着重研究了AlN-TiB₂导电陶瓷燃烧合成机理、导电性能和抗氧化性能。研究表明,随着导电相TiB₂含量的增加,产物的致密度、抗弯强度、硬度和断裂韧性均呈现先增加后降低的趋势,在TiB₂含量为45%时出现峰值。这是由于在燃烧合成反应区熔融的Al在TiB₂表面漫流,发生强烈的液相烧结,同时在外部压力作用下实现致密化。Al与TiB₂的比例过高或过低均不利于液相烧结的进行。同时,随着导电相TiB₂体积含量的增加,产物的电阻率下降。TiB₂体积含量为30⁶0%时,AlN-TiB₂体系具有良好的导电性,电阻率位于1800¹50μ?·cm之间。其次,本文采用原位合成的方式（B4C+Si BN+SiC）引入BN相,利用TiN和TiB₂相近的物理性能,同时为了降低反应的复杂性（TiB₂+N2 TiN+BN）,以TiN替代TiB₂,燃烧合成制备具有良好力学性能和导电性能的AlN-TiN-BN复合导电陶瓷。热力学分析表明,在100MPa反应压力下,燃烧温度较低时, TiN为稳定相;当燃烧温度较高时,将发生TiN+B4C TiC+TiB₂+N2的反应,产物的X射线衍射分析验证了上述的分析。导电相TiN含量对力学性能和电阻率的影响与AlN-TiB₂体系类似。另外,随着AlN-TiN-BN体系中原位生成的BN含量的增加,产物的致密度和强度下降,但产物的抗热震性显著提高。当BN含量为30%、40%时,产物的残余强度随热震温差的增加未发生明显的变化,抗热震性能优良。最后,为改善AlN-TiB₂复相导电陶瓷的力学性能,在AlN-TiB₂体系中加入SiC,研究AlN-SiC固溶强化对产物性能的影响。研究表明,在燃烧合成高温下,产物中AlN-SiC完全固溶。随着SiC含量的增加,一方面固溶强化作用增强;另一方面随着SiC含量的增加,Al含量下降,致密化过程减弱,在正反两方面因素作用下,产物的致密度、抗弯强度呈现先增加后降低的规律,在SiC含量为35%时出现峰值。对AlN-SiC-TiB₂体系的燃烧合成产物进行了热处理,研究了热处理温度（600-1200oC）和保温时间（1-10h）对产物性能和微观结构的影响。随热处理温度的升高和保温时间的延长,陶瓷试样的力学性能得到显著提高,得到了抗弯强度达517.8MPa、断裂韧性5.79MPa?m1/2、洛氏硬度94.1、致密度达95%的AlN-SiC-TiB₂陶瓷。研究了热处理产物的表面背散射相和透射相,结果表明:存在明显的AlN-SiC分相现象并在AlN基体和TiB₂颗粒的界面处观察到大量的纳米尺寸的TiB₂晶体析出相。热处理工艺增韧增强机理主要有:一是热处理工艺减弱或消除了存在于燃烧合成试样中的热应力;二是热处理后,固溶体的分相析出的富SiC相固溶体起到了颗粒弥散强化的作用;三是AlN-SiC基体中析出的TiB₂纳米晶粒,使晶格畸变降低,内应力得以释放,提高了产物的力学性能。另外,还研究了AlN-TiB₂体系和AlN-SiC-TiB₂体系的恒温氧化行为,两者的氧化增重与时间的关系均符合抛物线规律,后者的氧化速率和氧化层厚度远低于前者,抗氧化性能明显优于前者。两者的低温氧化产物以金红石结构的TiO2为主,AlN-TiB₂体系的高温氧化产物为Al2TiO5,氧化产物Al4B2O9、Al18B4O33的形成使得AlN-TiB₂陶瓷具有良好的自愈合性,因而AlN-TiB₂陶瓷具有良好的抗氧化性;而AlN-SiC-TiB₂体系的高温氧化产物以高强、低模量、低热膨胀系数的长棒状莫来石Al6Si2O13晶相为主,使其具有优异的抗高温氧化性能。更多还原

【Abstract】 The conductive ceramics is a kind of high-performance functional material, which combines the electrical properties of metal and structural properties. Therefore it has many advantages over common metal in certain physicochemical properties. In this paper, based on the reaction Al+N2 AlN, with the proportional additive of TiB₂ or TiN conductive phase, AlN-based conductive ceramic has been fabricated by the technology of combustion synthesis under the 100Mpa nitrogen atmosphere. Through adjusting the ratio of conductive phase and insulating phase, high temperature conductive ceramic with different conductivity can be obtained. Because each composition in this new composite ceramic has a high melting point, this sort of conductive ceramic system has some special features like good high temperature properties, excellent corrosion resistance and anti-wear property.Firstly, much more focuses have been paid on the combustion synthetic mechanism, conductive property and anti-oxidation property of AlN-TiB₂ composite conductive ceramics. Some researches show that: with the increase of the content of TiB₂, material properties just like relative density, Rockwell hardness, flexural strength and fracture toughness have the similar tendency of first increment and later decrement. And when the TiB₂ content is up to 45%, all mechanical properties have reached the peak value. This regularity can be explained by the densification mechanism. In the combustion synthesis reaction region, the melting Al will overflow on the surface of TiB₂ and strong liquid sintering will happen. At the same time densification can realize under the action of external pressure. Also with the increase of volume content of TiB₂ conductive phase, the electrical resistivity of samples decreases. When the volume content of TiB₂ is between 30% and 60%, the AlN-TiB₂ system has a good conductive property and the conductivity is around 1800¹50μ?·cm.Secondly, the method of in situ synthesis is used to introduce the BN phase （B4C+Si BN+SiC）. Meanwhile in order to reduce the complication of reaction TiB₂+N2 TiN+BN, TiN is used to replace the TiB₂ and a new composite ceramic AlN-TiN system is obtained. The results of thermodynamic analysis show that when the reaction occurs under high pressure （100Mpa） and low combustion temperature, TiN is a steady phase. While under high combustion temperature, the reaction of TiN+B4C TiC+TiB₂+N2 will happen. In fact the XRD results also validate the above analysis. And the influence of TiN content on the mechanical property and electrical resistivity of samples is similar to the AlN-TiB₂ ceramic system. With the increase of BN content, the relative density and strength of sample decrease, however the thermal shock resistance has been greatly improved. When the BN content is 30% or 40%, the residual strength of sample change little with the increase of heat shock temperature difference and it shows an excellent property of thermal shock resistance.Finally, SiC powders are introduced into the AlN-TiB₂ system to getting AlN-SiC-TiB₂ composite ceramic system and the solution strengthening effect of AlN-SiC to the sample property is studied. Research results show that AlN-SiC in the sample is fully solid solution under the high temperature during the combustion process. With the increase of SiC content, on the one hand, the solid solution effect increase, while on the other hand due to the decrease of Al content, the densification procedure is weakened. So with these cons and pros, the relative density and flexural strength both have a regularity of first increase and later decrease. Especially, when the SiC content is 35%, all the properties reach the peak value.Heat treatments are carried to improve the properties such as mechanical property and microstructure of AlN-SiC-TiB₂ sample after 600-1200℃for 1-10h. Obviously, with the temperature increasing and the prolongation of holding time, the mechanical properties have been greatly improved. AlN-SiC-TiB₂ composite ceramic has been fabricated by the optimum technology, whose relative density is 95%, flexural strength is high to 517.8MPa, fracture toughness is 5.79MPa?m1/2 and the Rockwell hardness is 94.1. Another studying in XRD and SEM show that: there is obvious phase separation is observed and this phenomena is becoming more and more intensified with the increase of heat treatment temperature and holding time. More importantly, the TEM results indicate that there is a lot of nano-scale TiB₂ crystal precipitated phase in the interface of AlN and TiB₂ particles.Accordingly, three different kinds of toughening and reinforcing mechanism of AlN-SiC-TiB₂ system have been discussed. The first one is that heat treatment technology has reduced the thermal stress in the combustion samples, the second one is after heat treatment the rich SiC from the phase separation of solid solution phase will have a function of particles dispersion strengthening. The third one is the uniform distribution of nano-scale TiB₂ which is precipitated between the AlN and TiB₂ particles phase interface, so a kind of composition gradient effect is formed between two phases to highlight the fracture toughness of samples.In addtion, the oxidation behavior under the constant temperature of AlN-TiB₂ and AlN-SiC-TiB₂ composite ceramics is studied. The oxidation experiment results show that: the relationship between oxidation weight gain and oxidation time satisfies the parabolic law. The oxidation rate and the scale thickness of AlN-SiC- TiB₂ system increase at a slow rate with the increase of oxidation temperature, and its oxidation resistance have advantage over the AlN-TiB₂ system. The low temperature oxidation products of both system are mainly rutile structure TiO2. In addition the formation of Al4B2O9、Al18B4O33 makes the AlN-TiB₂ ceramic has a good property of self-sealing and the high temperature oxide of AlN-TiB₂ is Al2TiO5. The high temperature oxidation products of AlN-SiC-TiB₂ system are Al6Si2O13 with long rods, which have specific properties such as high strength, low modulus and low thermal expansion coefficient. Therefore both composite ceramics have good anti-oxidation property.更多还原