Mechanism of Infiltration

Analytical treatments to describe fluid flow and heat transfer during infiltration of porous preforms by a liquid metal have been addressed by different groups at MIT (Ref 54, 55, 56, 57, 58, 59, 60, 61) and Colorado School of Mines (Ref 62) in the United States, also in England (Ref 63), France (Ref 64), Japan (Ref 65), China (Ref 66), and Jordan (Ref 67). General expressions have been derived to describe heat, mass, fluid flow, and kinetics during the infiltration process. A review of theoretical factors and mechanisms dealing with infiltration of a porous body by a liquid metal is given in Ref 68. Factors that control the matrix grain size, interfacial reactions, and morphology of the fiber-matrix interface and its stability have been predicted (e.g., initial fiber temperature, preform compressibility, reaction heat, external cooling, or reaction kinetics) (Ref 54, 57, 59, 70). Infiltration kinetics, size of the remelting region, and temperature distributions can be calculated (Ref 54, 58, 61, 62, 65, 70).

Models for pressure effects in conventional or new infiltration processes (squeeze casting or chemical vapor infiltration) have been developed (Ref 54, 57, 60, 61, 67, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80). Based on the analysis of physical phenomena that govern the infiltration process, good practical guidelines to optimize the processing techniques and the materials produced can be found in Ref 75.

The mechanism of wetting and spreading of the liquid metal has been studied (Ref 54, 78, 81, 82). These studies reveal the formation of a precursor film ahead of the bulk liquid front by adsorption, condensation, and surface migration on the solid wall (Ref 82). A model for chemical vapor infiltration is presented in Ref 83 and 84.

Sensors and models apparatuses (e.g., noninvasive capacitance technique), model experiments, and instrumented casting facilities have been developed to confirm theoretical predictions (Ref 55, 56, 58, 60, 64, 78, 81, 85, 86, 87). Modeling of magnetic field assisted and ultrasonic infiltration also has been attempted (Ref 88, 89, 90). A validation of the Lorenz force model has been experimentally obtained (Ref 88).

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