Characterisation of boron nitride fibre coatings with different crystalline order by TEM and XPS

Reinforcement effects in composites are widely influenced by fibre coatings . A detailed understanding of their microstructure and chemical composition is of great interest. Boron nitride films were deposited continuously on f ibre rovings of various ceramics in CVD reactors of vertical as well as hor izontal position. XPS depth profilings show that the film compositions are close to stoichiometric BN with carbon and oxygen impurities in the range o f 10 at%. Cross-sections of separated fibres were investigated by HREM and TEM diffraction. All BN films are hexagonal turbostratic. The (002) layers with an increased distance (about 0.36 nm) showed a mean stacking sequence near to graphite and a characteristic orientation to the fibre in the inter face region. We assume the gas flow type and hence the exchange rate of mat ter and energy determines the film structure in this region. With increasin g film thickness the (002) layers fold randomly in all directions or form n anocrystals at elevated temperatures.