PREPARATION AND HIGH TEMPERATURE OXIDATION BEHAVIOR OF MoSi_2-SiC COMPOSITES.

MoSi_2基复合材料在高温区具有优异的抗氧化性能，在超高温领域有着广阔的应用前景。而MoSi_2是一种脆性材料，在低温区表现出活性氧化。据推测，添加SiC是最有效的力学性能的改善。本文采用放电等离子烧结法制备了MoSi_2-SiC复合材料，并对其力学性能和抗氧化性能进行了研究。本研究取得的主要结果如下：（1）采用放电等离子烧结法可以简单地制备出致密的MoSi_2-SiC复合材料。（2）SiC颗粒的加入对MoSi_2的力学性能影响不大，但对抗弯强度影响不大。由于Si的选择性氧化形成了SiO_2保护层，（4）多孔复合材料形成SiO_2保护层的时间比致密复合材料长;（5）在773 K低温氧化时，随着SiC含量的增加，氧化增重变小，但同时生成氧化钼和氧化硅。（6）致密试样在循环氧化中仍表现出优异的抗氧化性能，而多孔复合材料表现出很高的氧化增重。（7）MoSi_2-SiC复合材料具有优异的抗氧化性能，是一种很有前途的超高温材料。

MoSi_2-based composites are expected for ultra-high temperature applications, because of the outstanding oxidation resistance in high temperature region. However, MoSi_2 is a brittle material and shows active oxidation in low temperature region. It is speculated that the addition of SiC is most effective for the improvement of mechanical properties. In the present study, preparation of MoSi_2-SiC composites is tried by using a spark plasma sintering method and the mechanical properties and oxidation resistance of the composites were studied. The main results obtained in the present study are as follows : (1) Dense MoSi_2-SiC composites can be produced briefly by applying a spark plasma sintering method (2) The addition of SiC particles has little influence on mechanical properties of MoSi_2 except for flexual strength (3) In oxidation at high temperatures like 1773 K,all composites which are fully dense have excellent oxidation resistance by the formation of a protective SiO_2 layr based on the selective oxidation of Si, regardless of their SiC content (4) The porous composites take longer time than the dense ones to form a protective SiO_2 layr (5) In oxidation at low temperatures like 773 K,the weight gain by oxidation becomes lower with increasing SiC content, although molybdenum oxide and silicon oxide are simultaneously formed (6) Dense specimens demonstrated excellent oxidation resistance even in cyclic oxidation, while porous composites showed quite high weight gain (7) MoSi_2-SiC composite is a promising material as an ultra-high temperature material which has outstanding oxidation resistance.