Combined Effects of Exposure to Salt (NaCl) Water and Oxidation on the Strength of Uncoated and BN‐Coated Nicalon™ Fibers

The environmental stability of uncoated and boron nitride‐coated (BN‐coated) Nicalon fiber has been investigated by studying the effect of annealing in air at 1000°C (2 h) on the strength of the fibers. The results imply that uncoated and BN‐coated fibers both degrade in strength, with the BN‐coated fiber suffering a higher strength loss. The degradation is significantly enhanced if the fibers are exposed to salt (NaCl) water prior to the air anneal, if the concentration of salt is >0.5 wt%. The BN‐coated Nicalon fibers also have been studied at 800° and 900°C; the degradation in strength due to salt water exposure is greater at 800°C than that at 900° or 1000°C.