Development of Ceramic Based Nanocomposites with High Toughness and Strength at High Temperatures

在Al_2O_3/碳化硅、氧化镁/碳化硅、氮化硅/碳化硅、Sialon/碳化硅等复合材料体系中，通过常规的烧结工艺制备出纳米级的第二相弥散分布在晶界内的纳米复合材料。对这些纳米复合材料进行了透射电子显微镜/扫描电子显微镜观察和力学性能测试，得出了以下结论。1)该纳米复合材料的力学性能包括断裂强度提高了2~4倍。2)纳米粒子的分散显著提高了复合材料的高温力学性能和抗热震断裂性能。其中，Al_2O_3和Si_3N_4的蠕变抗力主要通过晶间纳米分散提高1000~10000倍。3)这些反常性能的改善归因于晶内纳米分散体对基质颗粒的强化和晶间纳米分散体对原子尺度结构的控制。4)最后，低压无…人们成功地开发了更多的烧结工艺，用这些纳米复合材料制造复杂形状的机械零件。然而，很明显，只有纳米复合材料技术不能突破陶瓷的脆性。因此，微纳混杂的概念，即通过用微米级的第二相进一步增强纳米复合材料来提高其断裂韧性的概念被应用到Sialon/SiC纳米复合材料体系中。选用长碳纤维作为微米级增强体。研究结果如下：5)用碳长纤维增强Sialon/3vol%碳化硅纳米复合材料，制得了超韧强韧陶瓷，其1500MPAM温度下的强度可达1000 Mpa以上，韧性可达20~25MPAm^&lt；1/2~ﾟ；6)利用该超陶瓷材料可以成功地制造出燃气轮机的某些部件。除这些结果外，还得到了以下实验结果。7)Si_3N_4/碳化硅和Al_2O_3/碳化硅纳米复合材料的刀具性能明显优于整体材料。8)明确了晶内/晶间纳米分散体对超TENS复合体系的增韧机理。较少

The nanocomposites, in which nano-sized second phases were dispersed within matrix grains and at grain boundaries, were developed in the composite systems such as Al_2O_3/SiC,MgO/SiC,Si_3N_4/SiC and Sialon/SiC by usual sintering techniques. The TEM/SEM observations and mechanical properties tests on these nanocomposites gave the following conclusions. 1) Mechanicalproperties including fracture strength was 2 to 4 times improved by this nanocomposite technology. 2) High-temperature mechanical properties as well as thermal shock fracture resistance was significantly improved by nano-sized particle dispersions. In special, the creep resistance of Al_2O_3 and Si_3N_4 was 1000 to 10000 times improved mainly by intergranular nano-sized dispersions. 3) These abnormal properties improvement was attributed to the strengthening of matrix grains by intragranular nano-sized dispersions and the atomic scale structure control by intergranular nano-sized dispersions. 4) Finally, the low pressure less … More sintering proccess to make complex-shaped machine parts from these nanocomposite materials were successfully developed.It was clear, however, that only nanocomposite technology could not break thorugh the brittleness of ceramics. Thus, the micro-nano hybrid concept, that is, the concept to improve the fracture toughness of nanocomposites by further-reinforcing them with micro-sized second phases, was applied to the Sialon/SiC nanocomposite system. The long carbon fiber was selected as the micro-sized reinforcement. The results are as follows : 5) The super tough and strong ceramics with the strength of over 1000 MPa at 1500ﾟC and the toughness of 20 to 25 MPam^<1/2> were developed by reinforcing the Sialon/3vol% SiC nanocomposites with the carbonlong fiber. 6) Some parts of gas turbine engine could be successfully fabricated from this super-ceramic material. In adition to these results, following experimental results were also obtained. 7) The Si_3N_4/SiC and Al_2O_3/SiC nanocomposites exhibited essentiallyt much better properties for cutting tools than the monolithic materials. 8) The toughening strenghening mechanisms by intra/intergranular nano-sized dispersions were made clear for the over-tens composite systems. Less