Study Of In-situ Synthesis Of SiC_p-WSi₂/MoSi₂ Composites

Molybdenum silicide is a 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.The geometric model for calculating the ternary and polytery system base on binary geometric model is the most extensive solution model in calculation of thermodynamics and phase diagram. Based on Miedema model and Chou's model for calculating the heat of formation of binary solution, the integral equation has been established for calculating the activity coefficient in intermetallics and ternary systems. The activity coefficient and activity for compents with different temperature in intermetallics and ternary systems Si-C-W, Si-C-Mo, Mo-W-Si and Mo-W-C were calculated with the equation. Thus, the thermodynamic prediction for Mo-Si-C-W quaternary system was conducted and the theoretic base for in-situ synthesis of SiC_p-WSi₂/MoSi₂ compotises was founded. The thermodynamic calculation indicates that three stable products including SiC_p,WSi₂ and MoSi₂ can be obtained by means of in situ reaction and hot press synthesis of the Si, Mo, W and C powders at 1800K, which was confirmed by experiments. It was predicated that the synthesis of the SiC_pWSi₂/MoSi₂ composites by the in situ reaction and hot press is feasible.Based on the research on alloying and compositing of MoSi₂ and the calculation of thermodynamics of Mo-Si-C-W quaternary system, SiC_p-WSi₂/MoSi₂ composites were fabricated by means of in situ reaction and hot pressing the Si, Mo, W and C powders. The mechanical properties of the composites were measured and the microstructure was observed by using optical microscope, scanning electron microscope and X-ray diffractometer. The effect of strengthening and toughening the composites was analyzed and the mechanism was discussed. The results showed that, in the SiC_p-WSi₂/MoSi₂ composites, the reinforcement SiC is distributed around and in the grains of matrix MoSi₂ and WSi₂ is dissolved into the MoSi₂. The co-strengthening of SiC and WSi₂ makes the mechanical properties of the SiC_p-WSi₂/MoSi₂ composites much higher. The flexural strength of 592MPa, fracture toughness of 5.9 Mpam^1/2 and Vicker's hardness of 19.4GPa were measured for the composites, which is respectively 5, 2.1 and 2.2 times higher than those of pure MoSi₂...