Strength and stability studies on mini-tow ceramic composites made with nitrided Nextel (TM) 312 fibers and silicon oxycarbide

Abstract

Nitridation of Nextel(TM) 312 alumino-borosilicate fibers produces a boron-nitride-rich surface layer which acts as a debond layer in ceramic composites. This interface-fiber system offers a low cost alternative to CVD deposition of coatings on alumina and silicon carbide fibers. Ceramic fiber composites were made with 6 infiltration/pyrolysis cycles of a nitrided multifilament Nextel(TM) 312 mini-tow, using Blackglas(TM) resin to produce a silicon oxycarbide matrix. In the as-prepared condition the Nextel-Blackglas(TM) mini-tow composites had a mean tensile breaking load of 53 Newtons, a coefficient of variation of 26%, and limited fiber pull-out. The Nextel(TM) composites were then heat-treated in air at 600°, 800°, and 1000°C to determine oxidation stability. After 600°C oxidation for 200 hours, the Blackglas(TM) Nextel(TM) composites retained 75% of the as-prepared tensile break load with a fibrous fracture surface. Oxidation for 24 hours at 1000°C and for 100 hours at 800°C reduced the retained tensile breaking load by 47% and 66% respectively, showing reduced strain-to-failure and distinct embrittlement of the composite.