Reaction mechanism between Si-Co alloys and glassy carbon substrates

Metal matrix composites are well-known structural materials. Among different techniques, one common route for their production is the reaction infiltration of the liquid metal into solid preforms or powders. The reaction infiltration process is driven by capillary forces, and controlled by the chemical reactions occurring at the liquid/solid interfaces. In fact, there is a large amount of evidences that suggests the chemical reaction as the limiting processes in infiltration. Molten Si-Me (Metal) alloys are known to wet carbon and for this reason they can infiltrate carbon preforms forming SiC based composite materials. In this work we propose a fundamental study of the reaction mechanisms occurring at liquid Si-Co/glassy carbon interface, on the basis of the experimental results obtained by wetting experiments [1]. The experimental data concerning the composition, the morphology and the thickness of the interfacial layer as function of time and temperature, have been used to determine the mechanisms of formation and growth of the layers. The discussion has been carried out on the basis of previous works regarding pure Si in contact with graphite substrates [2] and. the thermodynamic and diffusion equations, used to predict the growth kinetics have been extended from pure Si to the Si-Co system, taking into account the role played by cobalt. The growth kinetics here obtained have been compared to the thickness of the reaction layer measured during the experimental work, in order to determine the most realistic mechanism occurring at the liquid Si-Co/glassy carbon interface.