The manufacture of SiC-based composites is quite widespread, and currently different methods are employed to produce them. The most efficient method, taking into account the cost/performance ratio, is reactive melt infiltration. It consists in infiltrating liquid silicon into a porous preform that must contain carbon, so that SiC is produced during infiltration. In the present work, the synthesis of two SiC-based composite materials with very different applications and microstructures has been studied and optimized. In both cases, materials have been obtained with suitable properties for the selected applications. One of the materials studied is silicon carbide particles/silicon (SiCp/Si) for protection systems such as armor jackets, and the other one is carbon fiber/silicon carbide (Cf/SiC) for use in braking systems. For the optimization, the dwell time and the atmosphere (Ar or primary vacuum) were used as variables. It has been found that in both preforms, the optimum conditions are 1 h dwell time and a vacuum atmosphere at 1450 °C. The effect of these parameters on microstructure and infiltration kinetics are discussed.
The knowledge of thermophysical properties of liquid Co-Si alloys is a key requirement for manufacturing of composite materials by infiltration method. Despite this need, the experimental and predicted property data of the Co-Si system are scarce and often inconsistent between the various sources. In the present work the mixing behaviour of Co-Si melts has been analyzed through the study of the concentration dependence of various thermodynamic, surface (surface tension and surface composition) and structural properties (concentration fluctuations in the long-wavelength limit and chemical short-range order parameter) in the framework of the Compound Formation Model (CFM) and Quasi Chemical Approximation for regular solutions (QCA). In addition, the surface tension of the Co 22.5 Si 77.5 (in at %) eutectic alloy, that is proposed to be used as the infiltrant, has been measured by the pendant drop method at temperatures ranging from 1593 to 1773 K. The results obtained were discussed with respect to both, temperature and concentration, and subsequently compared with the model predictions and literature data.
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