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

采用常规烧结技术，在Al_2O_3/SiC、MgO/SiC、Si_3N_4/SiC和Sialon/SiC等复合体系中制备了第二相分散在基体晶粒内和晶界的纳米复合材料。通过对纳米复合材料的TEM/SEM观察和力学性能测试得出以下结论：1)纳米复合材料的力学性能（断裂强度）提高了2 ~ 4倍。2)纳米级颗粒分散能显著提高材料的高温力学性能和抗热冲击断裂性能。其中，Al_2O_3和Si_3N_4的抗蠕变性能主要通过晶间纳米级分散提高了1000 ~ 10000倍。3)这些异常性能的改善是由于晶内纳米分散体对基体晶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，成功地开发了用这些纳米复合材料制备复杂形状机械零件的低压、少、多烧结工艺。然而，很明显，仅靠纳米复合技术并不能突破陶瓷的脆性。因此，微纳杂化概念，即通过添加微尺寸的第二相进一步增强纳米复合材料的断裂韧性的概念，被应用于Sialon/SiC纳米复合材料体系。选用长碳纤维作为微尺度增强材料。结果表明：5)用碳纤维对Sialon/3vol% SiC纳米复合材料进行补强，得到了在1500℃时强度大于1000 MPa、韧性为20 ~ 25 MPam^<1/2>的超韧强陶瓷。6)利用这种超陶瓷材料可以成功地制造燃气涡轮发动机的部分部件。除上述结果外，还得到了以下实验结果：7) Si_3N_4/SiC和Al_2O_3/SiC纳米复合材料的刀具性能明显优于单片材料。8)明确了晶内/晶间纳米分散体对复合体系的增韧强化机理。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