INFLUENCE OF A CVD CARBON COATING ON THE MECHANICAL PROPERTY STABILITY OF NICALON SIC FIBER

A thin carbon coating was applied to Nicalon NLM 102 fibers with the objective of improving both the stability of fiber strength and the matrix interface characteristics for reaction-bonded silicon nitride (RBSN) composites. Fiber strength was decreased by the 1100°C CVD coating process, but the much more severe degradation that normally results from heat treatment at 1350°C in N2 was mitigated somewhat in the coated fibers. The carbon film was not strongly bonded to the fiber, and thus was favorable for composite toughening by debonding and pull-out. Fiber degradation was greatly reduced in the presence of silicon. Both coated and uncoated fibers heat treated in close proximity to Si powder at 1350°C in N2, simulating reaction-bonded silicon nitride composite processing, retained mean strengths of 1·6 GPa at 1 cm gage length. © 1989.