PREPARATION OF DISPERSED PHASE CERAMIC BORON-NITRIDE AND ALUMINUM NITRIDE COMPOSITE COATINGS BY CHEMICAL VAPOR-DEPOSITION

Dispersed phase ceramic composite coatings containing BN and AlN were prepared by chemical vapor deposition. The BN + AlN coatings were deposited on Al2O3 from the BCl3-AlCl3-NH3 reagent system in the temperature range of 700-degrees to 1200-degrees-C. Also, single-phase BN and AlN coating were prepared for comparison purposes. The composite coatings consisted of very small BN and AlN regions which were either crystalline or amorphous, depending on deposition temperature and reagent concentrations. For example, a composite containing AlN whiskers of less than 100-nm diameter in a matrix of turbostratic BN of 2-nm grain size was deposited at 1100-degrees-C and 20 kPa.