ATOMIC-FORCE MICROSCOPE IMAGING OF THE SURFACE-ROUGHNESS OF SCS-COATED AND TIB2-COATED SIC FIBERS AND UNCOATED SAPPHIRE FIBERS

To understand the role of fibre surface roughness on the toughening of composite materials, it is imperative to characterize the fibre surfa ce structure properly. This paper presents nanometre scale images of t he surfaces of SCS- and TiB2-coated SiC fibres, and of uncoated sapphi re fibres, obtained by atomic force microscopy. It is found that SCS a nd TiB2 coatings deposited on SiC fibres using chemical vapour deposit ion methods produce fibres exhibiting surface structures that are tri- fractal over several decades of length scale. The sapphire fibre exhib ited a surface structure with two scales of periodic roughness, of wav elength 60 mu m and 100 nm. A roughness analysis of the experimentally obtained data at different resolutions demonstrated that the magnitud es of the conventional parameters root mean square (r.m.s.) height sig ma, r.m.s. slope sigma', and r.m.s, curvature sigma '' for the same su rface varied in some cases by more than an order of magnitude.