The diffusion of lead toward the interface of a rapidly solidified carbon fiber reinforced aluminum-lead matrix composite

The controlled precipitation of lead from a supersaturated aluminum-lead alloy was investigated as a means of controlling interface properties in aluminum/carbon fiber metal matrix composite. To this end, carbon fiber reinforced aluminum-lead metal matrix composites were produced using three techniques, namely, hot pressing (diffusion bonding), single-roller rapid solidification processing, and double-roller rapid solidification processing.; Composites formed by hot pressing fibers between strips of rapidly solidified aluminum-lead ribbon showed lead precipitation at the fiber/matrix interface when examined in cross-section with Energy Dispersive X-ray Spectroscopy.; Single-roller rapid solidification of composites was carried out by attaching fibers to a single rotating chill surface upon which a molten aluminum-lead solution would be ejected. Such rapidly solidified composite ribbons contained only a very few fibers, due to poor wetting of the fibers by the melt. Wavelength Dispersive X-ray Spectroscopy showed that the precipitation of lead was suppressed. Subsequent thermal annealing could, however, initiate precipitation.; To increase the volume fraction of fibers, an apparatus with two contacting chill surfaces was constructed. Composites produced with it included more fibers than those produced with the single-surface apparatus, while still suppressing the precipitation of lead. Thermal processing of these composites was investigated as a means of increasing the amount of lead at the fiber/matrix interface in a controlled manner. The lead concentration at the interface was found to increase, but the increase did not continue with further thermal processing.; Indentation tests on composite cross-sections showed some improvement in the fiber/matrix bond as a result of this thermal processing, compared to the composite as prepared. Dissolution of the matrix material showed that the lead coating on the fiber is not uniform.; Modeling of precipitation using a numerical solution of Ham's diffusion theory was carried out. It showed that if lead precipitation at the fiber/matrix interface was fed by migration of lead toward the fiber, then the region from which the lead was drawn must be small, much less than 75 {dollar}mu{dollar}m in radius.