ENVIRONMENTAL DURABILITY OF BN- BASED INTERPHASES (FOR SiC_f/ SiC_m COMPOSITES) IN H_2O CONTAINING ATMOSPHERES AT INTERMEDIATE TEMPERATURES

摘要

The effect of H_2O containing environments onthe stability of BN interphases was assessed for several BN-based interphases fabricated by different routes. Hi-Nicalon orNicalon fiber, CVI SiC matrix minicomposites with BNinterphases that were deposited at different temperatures (1050to 1800 deg C) or doped with Si were subjected to ends-onoxidation in a variety of H_2O/O_2 containing environments atintermediate temperatures (700-800 deg C) and times (1-100h).The samples were observed qualitatively to determine if the BNinterphase had volatilized, formed a glass, or remained intact.Several samples were longitudinally polished to determine thedistances of BN recession. It was found that the higher the BNprocessing temperature the more durable the BN in the H_2Ocontaining environments. Si-doping the 1400 deg C BN resultedin about the same durability as the 1800 deg C BN.