The fiber coating morphology in the composite was investigated by
TEM analysis in Fig. 4. The coating had a homogeneous thickness and
was composed of BN with scattered dark particles identified as Si3N4
and Si–C–B–N–O, Fig. 4c–e. High resolution TEM images of the interfaces
between coating and matrix, and between coating and fiber, are
reported in Fig. 5. It can be observed that the interface between coating
and matrix is sharp and clean, Fig. 5a–c, while the boundary between
fiber and coating was not clear and an amorphous phase seems to be
present, Fig. 5d–f.