The spreading kinetics of molten aluminum on ceramic surfaces bearing reactive coatings has been studied through the direct observation of sessile drops, either formed in situ or emplaced at temperature. Analysis of videotapes permitted the assessment of the rate of advance of rapidly spreading droplets. Experimental conditions in this study were chosen to avoid the severe retarding effect of the aluminum oxide film which is typically encountered in aluminum wetting experiments. A variety of reactive coating systems were examined (B, Cu, Ni, Ti, and Ti + B), and the effect of coating amount was assessed. Based upon the experiments of this study, the main effect of the coatings is to drive spreading due to strong exothermic interfacial reactions. The intensity of the interfacial reaction causes the change in free energy per unit area of interface to dominate the rate of movement of the triple line.

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Carbon fibers were treated with siloxane spin-on-glass and reaction bonded silicon oxycarbide coatings. The spin-on-glass (SOG) coatings were prepared by pyrolyzing solutions of polymethylsilsesquioxane (PMSO), polydimethoxysilane (PDSO), and poly(ethoxysilane)ethyltitanate copolymer (ESET). Since the flexibility of the coatings was found to be dependent on the concentration of the siloxane solution, only those of PMSO and PDSO below 1.25% were determined to be suitable for fiber coatings, and an alternative approach to the formation of a pliable silicon-based ceramic coating on the fibers was developed. Carbon fiber tows were impregnated by ethanolic solutions of organosilicon chlorides and fired at temperatures up to 900 °C to form a flexible reaction bonded silicon oxycarbide (RB-SiOC) coatings. Uncoated, SOG coated, and RB-SiOC coated carbon fibers were embedded in aluminum metal at 1000 °C. While both silica-based coatings protected the carbon surface, no wetting was observed, leading to fiber pull-out. When the coated fibers were treated with a mixture of Ti and B prior to immersion into the molten aluminum, complete wetting of the fibers occurred. In the presence of molten aluminum, the Ti/B coating enabled the exothermic formation of TiB 2 and titanium aluminides, which facilitate wetting. This reaction is termed ASPIRE (Aluminum Self-Propagating Interfacial Reaction) and in combination with silicon-based ceramic coatings provides a scientific approach to the formation of stable carbon fiber/aluminum metal-matrix composites. The coated fibers and composites were characterized by scanning electron microscopy (SEM) with energy dispersive x-ray (EDX) analysis, and x-ray photoelectron spectroscopy (XPS).