【作者】 王林；

【导师】 张立同； 徐永东；

【作者基本信息】 西北工业大学 ， 材料学， 2004， 硕士

【摘要】 自增韧是近年来发展起来的能够有效提高陶瓷断裂韧性的一种新型工艺。自增韧Si₃N₄陶瓷制备工艺简单、成本低廉、性能优异，愈加受到研究者们的关注。以Y₂O₃-La₂O₃为烧结助剂的自增韧Si₃N₄，可作为高温结构部件的候选材料。 本文研究了热压烧结工艺、气压烧结工艺对Si₃N₄显微结构、致密化的影响，分析了烧结工艺和显微结构、致密化的关系，讨论了机械加工对Si₃N₄抗弯强度的影响。主要研究结果如下： （1）选择等摩尔Y₂O₃和La₂O₃作为烧结助剂，利用热压烧结的方法制备致密的自增韧Si₃N₄陶瓷，其相对密度高达99.8％，在1800～1840℃烧结1～2h可得到相对密度超过99％的Si₃N₄。 （2）通过调整热压烧结工艺，研究了Si₃N₄粒径及长径比的分布规律。在1640～1700℃范围内，较低的预烧温度会形成粒径较大、长径比较高的晶粒，而较高的预烧温度会形成较均匀的显微结构；终烧温度升高能够促进氮化硅晶粒生长，氮化硅粒径及长径比均增大；延长烧结时间有利于提高晶粒的长径比，使粒径分布范围扩大。 ‘ （3）气压预烧结Si₃N₄过程中，气压烧结炉内温度过高导致烧结过程中出现伴生现象，分析了伴生物（如：晶须）的成分，发现烧结过程中出现的SiC晶须遵循VS生长机制。 （4）使用热压烧结炉进行气压预烧结试验，对气压预烧结工艺与Si₃N₄显微结构和致密化的关系进行了研究。在1800℃进行气压预烧结后，Si₃N₄的致密度未能达到下一步烧结所需要的密度，需要进一步提高烧结温度，同时升高气氛压力，防止Si₃N₄高温分解；试样第一次烧结时的温度越高，则其粒径和长径比越大。 （5）气压烧结用填粉进行多次预烧后，填粉中部分Si₃N₄与石墨发生反应生成SiC，填粉可以多次重复使用。 （6）对Si₃N₄陶瓷分别进行了切割、磨削、砂纸打磨、抛光处理，发现金刚石刀片切割材料会造成材料表面损伤，形成表面微裂纹，以较高的速度进行切 西北工业大学工学硕士学位论文 一 割所形成的表面缺陷少；抛光处理能够有效减少Si3N4陶瓷的表面缺陷，提高 Si3N4陶瓷的性能；在此基础上建立了Si3N4材料切削时的受力模型。更多还原

【Abstract】 The in-situ toughening is a new process developed recently, which can efficiently improve the fracture toughness of ceramics. Currently, the worldwide attention has been focused on the research of in-situ toughened Si3N4 because of its simple manufacturing techniques, low cost, and excellent performance. The in-situ toughened Si3N4 with Y2O3-La2O3 as additives is a candidate of thermal-structure components.Effects of hot-pressure sintering processes and gas-pressure pre-sintering processes on the microstructure and densification of silicon nitride are investigated in this thesis. The relations between sintering processes and microstructure, densification are analyzed. Influences of machining on the flexure strength of Si3N4 are discussed. The main results of investigation are as follows:(1) By hot-pressing sintering with equimolar Y2O3 and La2O3 as additives, a dense in-situ toughened Si3N4 is prepared. Its density is achieved 99.8 percent of theory density (To) of Si3N4. While Si3N4 over 99 percent To can be prepared by sintering for l~2h at 1800-1840℃.(2) By adjusting sintering processes, the rules of distribution of size and aspect ratio of silicon nitride crystals are investigated. Lower pre-sintering temperature would benefit forming crystals with bigger size and larger aspect ratio within extent of 1640~1700癈, higher pre-sintering temperature would form regular microstructure. Elevating final sintering temperature could accelerate the growth of crystals, with increasing the size and aspect ratio of crystals; meanwhile prolonging final sintering time is of benefi to increasing aspect ratio of crystals, and enlarging the distribution of size.(3) During gas-pressure pre-sintering, the temperature of gas-pressure sintering oven was too high, which leads to some accompanying phenomena. Components of the accompanying thing (for example: whiskers, sinter) are analyzed, the results are shown that the growth of SiC whiskers follow the mechanism of VS.(4) Conduct gas-pressure pre-sintering experiments in hot-pressure sintering oven, and investigate the relation between gas-pressure sintering processes and microstructure, densification of Si3N4. After gas-pressure pre-sintering at 1800℃, the density of Si3N4 don’t attach the value which adapt to next step sintering, and the pre-sintering temperature is needed to elevate with higher nitrogen pressure which to prevent the decomposition of Si3N4 in elevated temperature. The higher the first sintering temperature is, the larger the crystals size and aspect ratio are.(5) After several gas-pressure pre-sintering, Si3N4 in powder bed reacts with graphite, and creates silicon carbide. Powder bed could be used repeatedly.(6) After treatment of cutting, grinding, gritting and polishing, defaults on the surface of Si3N4 sample are created by diamond reamer during cutting. There are a few of surface faults created by reamer in high linear velocity. Surface faults of samples are efficiently reduced after polished. A model of Si3N4 suffering force during cutting is established.更多还原