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

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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.