The effect of siloxane spin-on-glass and reaction bonded silicon oxycarbide coatings with a self-propagating interfacial reaction treatment (ASPIRE) in the synthesis of carbon/graphite fiber-reinforced aluminum metal matrix composites

Abstract

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).

Effect of holding pressure on densification and mechanical properties of Cf/Mg composites

“…All of these were beneficial to play the full load-carrying role of carbon fibres, which could be seen in the stress-stain curve [29]. The contact angle θ between carbon fibres and molten magnesium alloy was more than 90°, so the solidification interface would be bulged, and the tip of the dendrite growth tendency was located in the space between adjacent carbon fibres [30]. When the holding pressure was too high, the damage on the carbon fibres occurred, which directly reduced the mechanical properties of Cf/Mg composite materials [31].…”