PREPARATION OF Mo-Si-C ULTRA-HIGH TEMPARATURE COMPOSITES.

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MoSi_2, SiC and C are promising materials for ultra-high temperature applications. Therefore, combination of those materials could produce new ultra-high temperature composites. In the present study, preparations of the MoSi_2-SiC composites and the graphite-MoSi_2 joints were carried out by powder metallurgy with a spark plasma sintering equipment.MoSi_2-SiC composites : Fully dense MoSi_2-SiC composites can be produced briefly by applying a spark plasma sintering method. When mixed powders of MoSi_2 and SiC are used for the preparation of MoSi_2SiC composites, aggregation of SiC is liable to occur. On the other hand, uniform disparsion of SiC is achieved by using mixed powders of Mo, Si and C as starting materials. The reaction process and the sintering behavior of the mixed powders of Mo, Si and C were also clarified by DTA experiments and thermal expansion-shrinkage measurements during sintering. The prepared composites have outstanding oxidation resistance. In particular, it is very important finding that the composites prepared from the mixed powders of Mo, Si and C don't show simultaneous oxidation of Mo and Si even in the accelerated oxidation region. It is concluded that MoSi_2-SiC composite is a promising material for ultra-high temperature applications.MoSi_2-graphite joints : The graphite-MoSi_2 joints having high flexural strength is prepared by using a plasma sintering equipment. However, the flexural strength depends on the thickness of a SiC layr which is formed in the interfacial reaction between MoSi_2 and graphite. The formation of SiC can be suppressed completly by inserting a Ti foil between tham.