【作者】 胡继林；

【导师】 肖汉宁；

【作者基本信息】 湖南大学 ， 材料学， 2014， 博士

【摘要】 碳化硅（SiC）陶瓷由于具有高温强度高、高温抗氧化能力强、热导率高、化学稳定性好等一系列优异性能，在机械、化工、能源和军工等领域得到广泛的应用。然而，由于SiC陶瓷存在室温强度与断裂韧性较低以及对缺陷的高度敏感性等方面的不足，限制了它更广泛的应用。在SiC基体中引入过渡金属硼化物或碳化物作为第二相弥散强化是解决这些问题的一个有效方法。通常，SiC-TiC或SiC-TiB2复相陶瓷材料的制备是通过直接将SiC和TiC或TiB2粉末混合后采用热压或常压烧结。然而，机械混合粉末会带来所制备的SiC-TiC(TiB2)复相陶瓷材料中的成分不均匀性，从而会导致对SiC-TiC(TiB2)复相陶瓷材料的性能带来不利的影响。本文针对上述问题，首先开展了SiC-TiC和SiC-TiB2复合粉末的合成与生长机理研究，进而对所合成的SiC-TiC和SiC-TiB2复合粉末进行烧结并对其相关性能进行研究。以硅溶胶、炭黑和TiO2为原料，采用碳热还原法在氩气气氛下合成了SiC-TiC复合粉末。研究了反应温度、TiO2添加量对合成SiC-TiC复合粉末的物相组成和显微形貌的影响；对反应过程进行了热力学分析和计算，探讨了SiC-TiC复合粉末的生长机理。结果表明：SiC-TiC复合粉末适宜的合成条件为在1600℃保温1h。在反应过程中，TiC先于SiC形成，TiC的形成抑制了SiC颗粒的生长。当复合粉末中TiC的含量为10%左右时，SiC的合成过程由气-固（V-S）反应转变为V-S和气-气（V-V）反应共同作用，复合粉末主要由球状颗粒、短棒状颗粒以及少量晶须组成。随着复合粉末中TiC含量的增加，SiC晶须的生长受到抑制，其形貌逐步由长纤维状向短棒状和颗粒状过渡。以SiC、TiO2和炭黑为原料，在真空条件下合成了SiC-TiC复合粉末。对合成SiC-TiC复合粉末的物相组成和显微形貌进行了表征，同时探讨了合成粉末样品的氧化性能。结果表明：在本实验条件下，SiC-TiC复合粉末适宜的合成条件为在1350℃保温1h。在SiC粉末中生成的TiC以粒径为0.1~0.2μm的小颗粒存在。SiC-TiC复合粉末在氧化过程中，TiC优先与氧发生反应生成TiO2，然后是SiC与氧反应生成SiO2。以硅溶胶、炭黑、TiO2和B4C为原料，采用碳热还原法在氩气气氛下合成了SiC-TiB2复合粉末。研究了反应温度、TiO2添加量对合成SiC-TiB2复合粉末的物相组成和显微形貌的影响，探讨了SiC-TiB2复合粉末的生长机理。结果表明：SiC-TiB2复合粉末适宜的合成条件为在1600℃保温1h。在反应过程中，TiB2先于SiC生成，TiB2的生成改变了SiC的生长方式。当复合粉末中TiB2的含量为10%左右时，SiC的合成过程由V-S反应转变为V-S和V-V共同反应，复合粉末主要由少量球状颗粒、短棒状颗粒以及大量的晶须组成。随着复合粉末中TiB2含量的增加，SiC晶须的生长受到抑制，合成产物中球状、片状和短棒状等结构的颗粒明显增多，出现结构多样化并存的现象。以SiC、TiO2、B4C和炭黑为原料，在真空条件下合成了SiC-TiB2复合粉末。研究了反应温度对合成SiC-TiB2复合粉末的物相组成和显微形貌的影响，同时对合成的SiC-TiB2粉末样品的氧化性能进行了探讨。结果表明：在真空条件下，合成SiC-TiB2复合粉末的合适反应条件为在1300℃下保温1h。SiC-TiB2复合粉末的氧化机理为：TiB2优先与氧发生反应生成TiO2和B2O3，然后是SiC与氧反应生成SiO2和CO。采用AlN和Y2O3作为烧结助剂，对以硅溶胶、炭黑和TiO2为原料合成的SiC-TiC复合粉末的烧结性能进行了研究，探讨了AlN和Y2O3的添加量对所制备的SiC-TiC复相陶瓷的致密度、硬度和显微结构的影响。结果表明：当AlN-Y2O3添加量为10vol%时，所合成的SiC-TiC复合粉末具有良好的烧结性能，该复合粉末经25MPa和1900℃热压烧结1h后，其烧结体的相对密度达到98.9%，洛氏硬度为93.2HRA。以TiO2、B4C、炭黑和SiC为原料，以AlN和Y2O3为烧结助剂，通过原位反应制备了SiC-20vol%TiB2复相陶瓷材料。探讨了不同添加量AlN和Y2O3对SiC-TiB2复相陶瓷的致密度、力学性能、电学性能以及显微结构的影响，分析了AlN-Y2O3的助烧结机理。实验结果表明：当烧结助剂的添加量为10vol%时，所制备的SiC-TiB2复相陶瓷的综合性能最佳，烧结样品的相对密度达到99.1%，抗弯强度为641MPa，硬度为91.8HRA，电阻率达到最小值为17.5mΩ·cm。从试样的断口中可看到晶粒拔出留下的痕迹，晶粒与晶粒之间的结合非常紧密，是赋予SiC-TiB2复相陶瓷优异综合性能的前提。更多还原

【Abstract】 Silicon carbide (SiC) has been widely used in machinery, chemical engineering,energy and many other industries due to its excellent combination of properties suchas high temperature strength, good oxidation resistance, high thermal conductivity,extreme chemical stability, etc. However, the application fields of SiC ceramics islimited by its low room-temperature strength, poor fracture toughness and high flawsensitivity. An effective method to solve the problems is to introduce transition metalboride or carbide into SiC matrix as strengthening phase. Generally, SiC-TiC andSiC-TiB2composites are prepared by directly mixing SiC and TiC or TiB2powdersand then hot-pressing or pressureless sintering. However, mechanical mixing of thepowders makes inhomogeneity of the SiC-TiC(TiB2) composites，resulting in anunfavourable inference on the properties of SiC-TiC(TiB2) composites. Based on theabove, this work intends to prepare SiC-TiC(TiB2) composite powders, andinvestigate synthesis, particle growth and sintering mechanism of SiC-TiC(TiB2)composite powders.SiC-TiC composite powders were synthesized in Ar by carbothermal reductionmethod using silica sol, carbon black and titanium oxide as raw materials. The effectsof reaction temperature and titanium oxide content on the phase composition andmorphology of SiC-TiC composite powders were investigated. The thermodynamicanalysis and calculation were performed systematically during the reaction, and thegrowth mechanism of SiC-TiC composite powders was discussed. The results showthat the suitable condition for synthesizing SiC-TiC composite powders is at1600℃for1h. In the reaction process, TiC formed ahead SiC, and the formation of TiCinhibits the grain growth of SiC particles. When TiC content is about10%, theformation of SiC is controlled from vapor-solid mechanism to the combinationvapor-solid and vapor-vapor mechanism. The composite powders are mainlycomposed of round-like particles, short rod-like particles and a small amount ofwhiskers. With the increase of TiC content in the composite powders, the growth ofSiC whiskers is inhibited and the morphology of SiC gradually transfers from longfiber to short rod-like and round-like particles.SiC-TiC composite powders were synthesized in vacuum using SiC, TiO2andcarbon black as starting materials. The phase composition and morphology of SiC-TiC composite powders were investigated and the antioxidation performance of SiC-TiCcomposite powders was discussed. Results show that the suitable condition forsynthesizing SiC-TiC composite powders is at1350℃for1h. The size of in-situcreated TiC particles is about0.1~0.2μm. In the oxidation process, TiC reacts inpriority with O2to form TiO2, then SiC reacts with O2to form SiO2.SiC-TiB2composite powders were synthesized in Ar by carbothermal reductionusing silica sol, carbon black, TiO2and B4C as raw materials. The effects of reactiontemperature and titanium oxide content on the phase composition and morphology ofSiC-TiB2composite powders were investigated. The growth mechanism of SiC-TiB2composite powders was discussed. The results show that the suitable condition forsynthesizing SiC-TiB2composite powders is at1600℃for1h. In the reaction process,TiB2formed ahead SiC, and the formation of TiB2alters the growth mode of SiC.When TiB2content is about10%, the formation of SiC is controlled from vapor-solidreaction to the combination of vapor-solid and vapor-vapor reaction. The compositepowders are mainly composed of a small amount of round-like particles, shortrod-like particles and lot of whiskers. With the increase of TiB2content in thecomposite powders, the growth of SiC whiskers is inhibited. And the number ofround-like, plate-shaped and short rod-like particles in the composite powdersincreases noticeably, which results in the variety of the morphology.SiC-TiB2composite powders were synthesized in vacuum using SiC, TiO2，B4Cand carbon black. The effects of reaction temperature on the phase composition andmorphology of SiC-TiB2composite powders were investigated and the antioxidationperformance of SiC-TiB2composite powders was also discussed. Results show thatthe suitable condition for synthesizing SiC-TiB2composite powders in vacuum is at1300℃for1h. In the oxidation process, TiB2reacts in priority with O2to form TiO2and B2O3，then SiC reacts with O2to form SiO2and CO.The sintering behavior of SiC-TiC composite powders synthesized bycarbothermal reduction using silica sol, carbon black and titania powders isinvestigated. The effects of the volume fraction of AlN and Y2O3on density, hardnessand microstructure of SiC-TiC composites were discussed. Results show that theSiC-TiC composite powders reveal good sinterability when the AlN-Y2O3adds isabout10vol%. The sample hot-pressed at1900℃for1h under25MPa, possesses arelative density of98.9%and Rockwell hardness of93.2HRA.SiC-TiB2composites with20vol%TiB2were fabricated by in situ reactionbetween TiO2, C and B4C，with AlN-Y2O3as sintering aids. The effects of the volume fraction of AlN and Y2O3on the density, mechanical properties, electrical propertiesand microstructure of the SiC-TiB2composites were determined. Results show thatSiC-TiB2composites possess the good comprehensive performance when the contentof sintering aids is10vol%, showing a relative density of99.1%, flexural strength of641MPa and Rockwell hardness of91.8HRA, respectively. The resistivity of theSiC-TiB2composites reaches17.5mΩ·cm at10vol%AlN-Y2O3. Pull-out of crystalparticles is observed from the fracture morphology of the composites. Tightly bondedgrains contributed to the excellent combination of properties of SiC-TiB2composites.更多还原