Composition and Microstructure of Chemically Vapor‐Deposited Boron Nitride, Aluminum Nitride, and Boron Nitride + Aluminum Nitride Composites

The composition and microstructure of dispersed‐phase ceramic composites containing BN and AIN as well as BN and AIN single‐phase ceramics prepared by chemical vapor deposition have been characterized using X‐ray diffraction, scanning electron microscopy, electron microprobe, and transmission electron microscopy techniques. Under certain processing conditions, the codeposited coating microstructure consists of small single‐crystal AIN fibers (whiskers) surrounded by a turbostratic BN matrix. Other processing conditions resulted in single‐phase films of AIN with a fibrous structure. The compositions of the codeposits range from 2 to 50 mol% BN, 50 to 80 mol% AIN with 7% to 25% oxygen impurity as determined by electron microprobe analysis.