Infiltration Kinetics Of Liquid Metals Into Porous Carbon Preforms

Carbon fiber reinforced SiC or Cu-SiC based composites are potential candidate materials for high temperature technologies. One of the main fabrication techniques for these composites is the liquid melt infiltration (LMI). The LMI is a fast and low-cost manufacturing process for structural components based on Si or Cu-Si alloys. The LMI begins by melting of the Si and Cu-Si alloy powder that encases the porous carbon preforms, and then continuous as liquid Si and Cu-Si alloy fills the pores of the carbon by reactive wetting. Melt infiltration is governed by the capillary action. Therefore, a good understanding of wetting behavior between Si and Cu-Si with the porous carbon preforms is important in understanding the infiltration kinetics and controlling the infiltration process. However, the infiltration behavior/kinetics is quite dependent on the composition of infiltration alloys, infiltration temperature, wetting angle and vacuum condition etc.Till now, there are several studies in the literature which have specifically addressed the capillary phenomena in aerospace engineering, as well as in biology or geophysical science. Although some infiltration of porous media experiments have been done, a systematic and comprehensive investigation of the kinetics of Si and Cu-Si alloy infiltration behavior in the porous carbon preforms is still lacking.The objective of this study is to carry out an investigation on liquid Si and Cu-Si alloy flowing through a porous carbon preforms. Firstly, the flow behavior of liquid Si and Cu-Si alloy infiltration process was simulated by a two-dimensional model under various parameters such as pore size of preform and infiltration rate on the wetting angle. Interfacial phenomena and the effects of small addition of silicon (Si), titanium (Ti) and Chromium (Cr) in Carbon/Copper (C/Cu) composites during liquid infiltrations are also discussed. The additions of Si, Ti and Cr into Cu melt promote the reactive wetting between liquid Cu alloy and carbon due to the formation of silicon carbides, titanium carbides and chromium carbides, respectively. The possible reactions and accompanying free-energies for the formation of silicon carbides, titanium carbides and chromium carbides are studied. Two-dimensional infiltration equations are developed using the Washburn equation in the limit of both interface and diffusion control:(?) for situations where the capillary radius decreases with time and the contact angle are assumed constant during infiltration, and (?) for both situations where the capillary radius decreases either linear or parabolic. The computational outcomes for the reactive penetration of carbon capillaries by Si and Cu-Si alloys show that greater lengths are attained at lower values of the parabolic rate constant. For both interface-limited and diffusion-limited capillary rise, the penetration lengths are larger. This work focuses on equilibrium and non-equilibrium wetting effects, and is a fundamental approach to these complex kinetic phenomena.