The high fabrication cost of ceramic-reinforced metal-matrix composites (CMMCs) has greatly limited their widespread commercial applications. Pressureless infiltration of a molten alloy into a ceramic preform is believed to be a promising way to fabricate CMMCs at low cost. In this dissertation, efforts were made to develop such a rapid pressureless infiltration technique for producing CMMCs and to understand the thermodynamics and kinetics involved in the pressureless infiltration process.; The thermodynamic criterion for a liquid to pressurelessly infiltrate into a porous medium was studied and the results show that a necessary condition for pressureless infiltration is that the wetting angle between the liquid and the medium must be substantially lower than 90{dollar}spcirc{dollar}, and this critical wetting angle is dependent on the packing density and the channel configurations of the porous medium.; A low-cost fabrication technique, referred to as rapid pressureless infiltration in air, has been proposed and developed for producing SiC reinforced Al-Si alloys. The rapid and pressureless infiltration is induced by a violent reaction between Si in the Al alloy and carbon (C) in the SiC preform. The fabrication process includes two steps, preform preparation and infiltration operation. A preform can be obtained by pressing a mixture of SiC powder and a polymer binder into a desired shape and subsequently pyrolizing the polymer binder into C. The infiltration operation was performed by dipping the pyrolized SiC preform into a molten Al-Si alloy in an open air environment.; The key factors that affect the infiltration process are found to be the infiltration temperature and the compositions of both the Al alloys and the SiC preforms. The conditions for achieving rapid pressureless infiltration are: the infiltration temperature higher than 1400{dollar}spcirc{dollar}C, a thin C coating on each individual SiC particles, and the presence of a sufficient amount of Si in the Al alloy.; The infiltration process is found to occur in two stages, the infiltration initiation and the infiltration propagation. The initiation of the infiltration is controlled by the partial pressures of oxidizing gases such as O{dollar}sb2{dollar} or CO at the infiltration front. The critical pressure of oxidizing gases is found to be on the order of 10{dollar}sp{lcub}-4{rcub}{dollar} atm for the systems examined in this study. The propagation stage operates in two different modes, a reaction-controlled mode and an infiltration-controlled mode. The reaction-controlled mode operates when the Si concentration at the infiltration front is sufficiently high, and the reaction product is SiC. The infiltration-controlled mode operates when the Si concentration is lower than a critical value, and the reaction product is dominantly elongated fine Al{dollar}sb4{dollar}SiC{dollar}sb4{dollar} grains.
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