A Process for Composite Fabrication by Silicon Slurry Coating of Continuous Fiber Tows

摘要

A process is described for coating continuous small-diameter fiber tows with silicon-filled polymer slurries. This can enable fabrication of complex shaped ceramic matrix composites such as those based on reaction-bonded silicon-nitride matrices.The coating process sequence includes sizing removal, drying, spreading, dip-coating, drying, and die consolidation to infiltrate a silicon-filled polymer slurry into interstices of the fiber tows. Sizing removal from the as-received fibers was accomplished by using an ultrasonic cleaner with water-isopropyl alcohol solutions at elevated temperatures (30 to 60 C). Measurements of surface tension, viscosity, and density of various slurry concentrations are listed. The coating thickness applied on the fiber surface can be correlated with the modified small wire theory. Optical microscopy of cross-sections of coated samples showed the degree of infiltration achieved. The overall diameters of the coated tows depended primarily on the drying (die) temperatures used in the drying furnace, which in turn appears related to the vapor pressure of the solvent evaporating at those temperatures. Finally, the effect of the coating process on the tensile strength of Nicalon fiber is also examined.