【作者】 田春艳；

【导师】 刘宁；

【作者基本信息】 合肥工业大学 ， 材料学， 2007， 博士

【摘要】 本研究以纳米Si₃N₄粉末作为原料，采用热压烧结方法制备了纳米Si₃N₄基陶瓷复合材料，运用XRD、SEM、TEM、EDX等手段对材料的显微组织进行了分析，研究了TiC、TiN、WC等第二相颗粒以及碳纳米管的添加对纳米Si₃N₄陶瓷力学性能的影响。首先，介绍了Si₃N₄陶瓷的组织性能、制备方法、增韧机理和发展趋势，并在此基础上指出了本文研究的目的和意义。其次，介绍了纳米Si₃N₄基陶瓷复合材料的制备工艺、力学性能的测试方法以及显微组织的表征方法。研究发现，将纳米Si₃N₄粉末进行超声分散，可以改善其分散状况；加入适量的表面活性剂能改善纳米Si₃N₄粉末的分散效果；分散体系的PH值也影响纳米Si₃N₄粉末的分散效果。纳米Si₃N₄陶瓷的主要组成相为α-Si₃N₄、β-Si₃N₄和Si₂N₂O，其组织由尺寸为100纳米左右的品粒组成。纳米Si₃N₄陶瓷的抗弯强度和断裂韧性均随α-Si₃N₄起始粉末含量的增加而先升后降，在其含量为40wt．％时达到最大值；硬度随α-Si₃N₄起始粉末含量的增加而降低。将TiC颗粒加入到纳米Si₃N₄陶瓷中，在液相烧结过程中，TiC与Si₃N₄发生反应，生成了TiC_0.7N_0.3。力学性能测试结果表明，添加适量的TiC颗粒可以提高纳米Si₃N₄陶瓷的抗弯强度和断裂韧性，当TiC的添加量为10wt.％时，抗弯强度和断裂韧性均达到最大值；纳米Si₃N₄陶瓷复合材料的硬度随TiC含量的增加而升高。纳米TiN颗粒与Si₃N₄基体之间有很好的化学相容性。添加适量的纳米TiN颗粒可以明显地提高纳米Si₃N₄陶瓷的抗弯强度和断裂韧性，抗弯强度和断裂韧性的最大值分别在纳米TiN添加量为10wt.％和15wt.％获得；纳米TiN颗粒的添加对纳米Si₃N₄陶瓷的硬度影响不大。纳米Si₃N₄-TiN陶瓷复合材料中的主要增韧机制为热膨胀失配增韧和裂纹偏转增韧。纳米Si₃N₄-WC陶瓷复合材料的硬度低丁纳米Si₃N₄陶瓷，但随WC含量的增加而逐渐升高。适量WC颗粒的添加可以提高纳米Si₃N₄陶瓷的断裂韧性和抗弯强度，其最大值分别在WC添加量为4wt.％和8wt.％时获得。CNTs-Si₃N₄纳米陶瓷复合材料的相组成主要为α-Si₃N₄、β-Si₃N₄和Si₂N₂O，碳纳米管在烧结过程中能保持良好的热稳定性。CNTs-Si₃N₄纳米陶瓷复合材料的抗弯强度和断裂韧性均随碳纳米管的含量的增加呈现先升后降的变化趋势，其最大值分别在CNTs含量为2wt.％和4wt.％时获得。碳纳米管含量为2wt.％时，硬度略有提高，然后随碳纳米管含量的继续增加而逐渐降低。碳纳米管增韧纳米氮化硅陶瓷材料的主要机制为碳纳米管的拔出、桥联和裂纹偏转机制。纳米氮化硅陶瓷的热震行为符合Hasselman的经典模型，起始粉末中适量α-Si₃N₄粉末的存在，能提高纳米氮化硅的抗热震性能。TiC颗粒的添加能改善纳米Si₃N₄陶瓷的热震抗力，添加了10wt.％TiC的纳米氮化硅陶瓷复合材料的临界温差△Tc最高，热震循环疲劳抗力最好。这是因为TiC的添加使裂纹产生钝化、偏转，消耗了更多的裂纹应变能，对裂纹的扩展有一定的阻碍作用。更多还原

【Abstract】 The Si₃N₄ matrix nano-ceramic composites were fabricated by hot press sintering using nano-Si₃N₄ powders. The microstructures were analyzed by means of XRD, SEM, TEM. EDX and so on. The effect of the second phases such as TiC、TiN、WC particles and CNTs on the mechanical properties of Si₃N₄ nano-ceramics were investigated.First, the microstructure, fabrication methods, mechanical properties, toughening mechanisms and development tendency of Si₃N₄ ceramics as well as the development status of nano-composite ceramics were introduced. Based on the above work, the purposes and significance of this thesis were pointed out. Secend, the fabrication techniques, the testing methods of mechanical properties and the observing methods of microstructure of Si₃N₄ matrix nano-ceramic composites were introduced.The research results show that the dispersion effect of nano-Si₃N₄ powders can be improved after being ultrasonically dispersed. The introduction of proper amount of surfactant can improve the dispersion effect of nano-Si₃N₄ powders. In addition, PH values of dispersing system also affect the dispersion effect. The main phases in Si₃N₄ nano-ceramics areα-Si₃N₄,β-Si₃N₄ and Si₂N₂O, and the SEM micrographs show that the microstructure of sintered materials consists of grains with approximate size of 100 nm. The flexural strength and the fracture toughness increase initially with the increase of the amount ofα-Si₃N₄ starting powders then decrease, and the maximum mechanical properties are obtained when the amount ofα-Si₃N₄ powders is 40wt.%. The hardness values decrease with the increase ofα-Si₃N₄ starting powders amount.The TiC particles that added as a dispersed phase react with Si₃N₄ during the liquid phase sintering, with the formation of TiC_0.7N_0.3. Adding proper amount of TiC particles can increase the flexural strength and the fracture toughness of Si₃N₄ nano-ceramics. The maximum values of the flexural strength and the fracture toughness were obtained when the amount of TiC particles is 10wt.%. The Vickers hardness of Si₃N₄ nano-ceramic composites increases with the increase of TiC amount.There is a good chemical consistency between TiN particles and Si₃N₄ matrix. The addition of proper amount nano-TiN particles can significantly increase the flexural strength and the fracture toughness. The maximum values of the fracture toughness and the flexural strength could be obtained when the amount of TiN particles was 10wt.% and 15wt.% respectively. However, the addition of nano-TiN particles has little effect on the hardness of Si₃N₄ nano-ceramics. The main toughening mechanism existing in Si₃N₄-TiN nano-ceramic composites are thermal expansion mismatch toughening mechanism and crack deflection toughening mechanism.The Vickers hardness of Si₃N₄-WC nano-ceramic composites is lower than that of Si₃N₄ nano-ceramics, while increases with the increase of WC amount. Adding proper amount of WC particles can increase the fracture toughness and the flexural strength of Si₃N₄ nano-ceramics. The maximum values of the fracture toughness and the flexural strength can be obtained when the amount of WC particles is 4wt.% and 8wt.% respectively.The main phases in CNTs-Si₃N₄ nano-ceramic composites areα-Si₃N₄,β-Si₃N₄ and Si₂N₂O. The carbon nanotubes can maintain good thermal stability during the sintering process of Si₃N₄ ceramics. The fracture toughness and the flexural strength initially increase with the increase of carbon nanotubes amount then decrease, and the maximum values of the fracture toughness and the flexural strength can be obtained when the amount of carbon nanotubes is 4wt.% and 2wt.% respectively. The Vickers hardness values has a little increase when the amount of carbon nanotubes is 2wt.%, then gradually decrease with the increase of carbon nanotubes amount. The main toughening mechanism existing in CNTs-Si₃N₄ nano-ceramic composites are pullout of CNTs, bridging of CNTs and crack deflection.The thermal shock behavior of Si₃N₄ nano-ceramics is similar to the mode of Hassalman. The existence ofα-Si₃N₄ starting powders can improve thermal shock resistance. The addition of proper amount TiC particles can improve the thermal shock resistance. When the TiC amount is 10wt.%, the critical temperature difference is highest and the thermal fatigue resistance is the best. It is because that TiC particles can induce crack passivation and deflection, which dissipates more crack strain energy and hinders the extension of thermal shock cracks.更多还原