Situ Sic Enhancement Of Mosi <sub> 2 </ Sub> Matrix Composites

Molybdenum silicide is one kind of intermetallic compounds, which has characters of metal and ceramic about structure and chemical bond. It can be applied not only as functional material, but also as structural material. This kind material has been received much attention in recent years for structural applications. The process of manufacturing MoSi₂ has been improved greatly.Based on the research on alloying and compositing of MoSi₂ and the theory of in situ synthesis, different volume fraction of SiC particle reinforced MoSi₂ composites (SiC_p/MoSi2) were manufactured by the in situ reactive hot pressing (technology I ) and by in situ reactive then hot pressing (technology II). The bending strength and the fracture toughness at room temperature of the composites were measured by means of the bending test of three point , vickers indentation test and oxidation test. The component of pure powder, the microstructure, the fracture morphology and the vickers indention of the composites were observed by means of scanning electron microscope, optical microscope and X-ray diffraction. The two kind of synthetic technology was compared. The effect of strengthening and toughening the composites was analyzed and the mechanism was discussed.The observations show that the technology I of manufacturing SiC particle-reinforced MoSi₂ composites is feasible. The microstructure and mechanical property of the sample manufactured by the technology I are approximately identical with those of the technology II. Additionally, the process of the former is much more simple, so it could save time and cost. The results show that the growth of MoSi₂ grain is prevented by SiC particles in the composites. Therefore, the mechanical property of the SiC_p/MoSi₂ composites is much higher than that of mono MoSi₂ at room temperature, and raised with increasing content of SiC to some extent. The experimental results indicate that the maximum bend strength and fracture toughnes were obtained from the composites with 40vol%SiC and 50vol%SiC, respectively. The formation of SiC particles increases the density of SiC_p/MoSi₂ composites, however, the density of the SiC_p/MoSi₂ composites was decreased when the content of SiC is more than 10%. The fracture morphology of the composites is of cleavage and brittle intergranular. The strengthening mechanism of this technology is fine grain and dispersion strengthening, while the toughening mechanism is fine grain toughening, bridging and the decreasing brittle matrix. The oxidation resistance property of MoSi₂ material is better than that of SiC_p/MoSi₂ composites at 400℃ ⁶00℃, and at 800℃¹200℃, the oxidation of MoSi₂ material and SiC_p/MoSi₂ composites is opposite.It is predicted that the techonology of in situ reactive hot pressing MoSi₂ composites based on the pure powders of Mo-Si-C has big potential in the future.