【作者】 肖光春；

【导师】 许崇海；

【作者基本信息】 山东轻工业学院 ， 机械电子工程， 2007， 硕士

【摘要】 本文针对成形模具对陶瓷材料的要求,从提高陶瓷模具材料的综合力学性能出发,选用具有高硬度、耐磨损、耐高温、抗腐蚀、原料分布广泛的Al₂O₃陶瓷为基体,采用纳米复合方法制备出具有较高综合力学性能的纳米复合陶瓷模具材料。从热压烧结工艺、微观结构及其与力学性能的关系等方面,系统研究了纳米复合陶瓷模具材料的增韧补强机理,发现晶内/晶间混合型的微观结构和穿晶/沿晶混合断裂模式,是纳米复合陶瓷模具材料强韧化提高的主要原因。根据胶体化学理论中的悬浮液的稳定机制,采用起空间位阻稳定作用的PEG为分散剂,对不同的纳米陶瓷粉体进行了液相分散研究,通过优化PEG分散剂的分子量、加入量以及悬浮液的pH值等参数,结合超声分散及机械搅拌工艺,得到了分散均匀的纳米粉体及其混合粉体的稳定悬浮液。探讨了组分含量、烧结工艺对纳米复合陶瓷模具材料微观结构和力学性能的影响,研制成功了纳米复合陶瓷模具材料Al₂O₃/Ti（C₇N₃）,其抗弯强度为789 MPa、断裂韧性为8.1MPa·m1/2、硬度16.4GPa。与单一的微米Al₂O₃陶瓷材料相比,其抗弯强度和断裂韧性都得到大幅提高。在致密的烧结陶瓷中,纳米Ti（C₇N₃）与微米Al₂O₃形成了典型的晶内/晶间混合型结构,裂纹从晶间到晶内再到晶间的路径扩展,消耗了更多的断裂能,形成了沿晶/穿晶混合的断裂模式,是其综合力学性能得到较大提高的主要原因。表面压痕裂纹的偏转和桥联及裂纹分支和颗粒拔出,是复合材料韧性提高的表现。对纳米复合陶瓷模具材料进行了摩擦磨损性能实验研究,并对其磨损表面微观形貌进行了观察和分析,探讨了Al₂O₃/Ti（C₇N₃）纳米复合陶瓷模具材料的磨损机理。研究结果表明,在法向载荷50～150N、摩擦转速为70r/min和140r/min干摩擦条件下,纯Al₂O₃陶瓷的摩擦系数为0.58～0.8,Al₂O₃/Ti（C₇N₃）纳米复合陶瓷模具材料的摩擦系数为0.45～0.65;纯Al₂O₃陶瓷磨损率的数量级为10-14m3/N·m,Al₂O₃/Ti（C₇N₃）纳米复合陶瓷模具材料磨损率的数量级为10-15m3/N·m;纯Al₂O₃陶瓷的磨损机理为脆性断裂和磨粒磨损,Al₂O₃/Ti（C₇N₃）纳米复合陶瓷模具材料的磨损机理为机械冷焊、塑性变形和磨粒磨损。更多还原

【Abstract】 From the requirement for ceramic materials of the forming dies, nanocomposite ceramic die materials with high mechanical properties were fabricated successfully with nanometer composite method by selecting alumina ceramic as matrix which has excellent hardness, wear-resistance, high-temperature resistance, corrosion resistance and wide range raw materials. The strengthening and toughening mechanisms of the ceramic die materials were investigated from the respects of the correlations among the hot pressing process, the microstructures and mechanical properties. It reveals that the intra/inter granular microstructures and the trans/inter granular fracture modes are the main causes for improving the flexural strength and fracture toughness.Based on the stabilization mechanisms for suspensions in the colloidal chemistry, the dispersion of different nano-scale ceramic powders in liquid suspension were discussed by steric stabilization with PEG dispersant. The homogeneous and dispersing nanometer powder and its suspensions were obtained by means of adding different molecular weight PEG, adjusting PEG quality percent and pH values with ultrasonic dispersion and mechanical mixing technology.The effects of component quantity and sintering technique to microstructure and mechanical properties of nanocomposite ceramic die materials were discussed. Nanocomposite ceramic die material of Al₂O₃/Ti（C₇N₃） was fabricated successfully, its flexural strength, fracture toughness and Vickers hardness are 789MPa, 8.1 MPa·m1/2 and 16.4GPa respectively. The flexural strength and fracture toughness are much higher than that of pure micron alumina ceramic material. The nano-scale Ti（C₇N₃） particles are located between or within Al₂O₃ matrix. Thus the typical mixture granular microstructure is formed in the dense compacts, which resulted in the mixture granular fracture modes. The zigzag crack path, which is from the grain boundary into the grain and then turning to the boundary, can result in higher consumption of fracture energy and the increase of fracture toughness. Crack deflection, crack bridging, crack branching and grain pull-out reveals the improvement of the fracture toughness of the composites.The wear mechanisms of nanocomposite ceramic die materials were discussed by analyzing SEM micrographs of wear tracks on typical specimens. It is indicated that in unlubricated conditions of normal load of 50N to150N and rotational speed of 70r/min and 140r/min the friction coefficient of pure alumina is in the range of 0.58～0.8, and the friction coefficient of Al₂O₃/Ti（C₇N₃） nanocomposite ceramic die material is in the range of 0.45～0.65. The wear rate of pure alumina is in the order of 10-14m3/N·m while that of Al₂O₃/Ti（C₇N₃） nanocomposite ceramic die material is in the order of 10-15m3/N·m. The dominant wear mechanisms of pure alumina may be brittle fracture and abrasive wear. While the dominant wear mechanisms of Al₂O₃/Ti（C₇N₃） nanocomposite ceramic die material may be mechanical interlocking and plastic deformation combined with a little micro-fracture and abrasive wear.更多还原