Surface roughness characterization of Nicalon^™ and HI-Nicalon^™ ceramic fibers by atomic force microscopy

The behavior of ceramic composites is governed by the nature of the fiber/matrix interface. Fiber surface roughness is a key parameter in the behavior at the fiber/matrix interface (e.g., debonding, interfacial sliding) and the overall behavior of a composite. Using an atomic force microscope (AFM), quantitative surface roughness values of ceramic fibers can be obtained, with an uncertainty of 1nm. The AFM technique was used to obtain surface roughness profiles and analysis on Si-C-O and Si-C fibers (Nicalon, and a new, virtually oxygen-free Si-C fiber, HI-Nicalon). The latter fiber had a slightly higher roughness amplitude, which may be caused by differences in processing. Although the differences in roughness between the fibers were small, the calculated radial strain and radial normal stress in composites reinforced with HI-Nicalon were higher than in those reinforced with Nicalon. This result indicates that small changes in the roughness of a fiber can significantly affect the debonding and sliding properties between the fiber and matrix.