Analysis of SiC fibres and composites using Raman microscopy

Abstract

SummaryThe application of Raman spectroscopy in the analysis of the microstructure of SCS-6 silicon carbide fibres using a Renishaw Raman microscope is described. It is demonstrated that the technique allows a detailed study to be made of the point-to-point variation in microstructure across a fibre section. It has been possible to monitor the variation of the concentration of SiC and carbon in the fibre microstructure and to detect differences in the forms of carbon present. It is also shown that Raman spectroscopy can be used to follow the micromechanics of both the deformation of silicon carbide fibres and of the fibres within a model composite. Well-defined Raman spectra have been obtained from a variety of Nicalon and Tyranno fibres and the positions of the Raman bands shown to shift on the application of stress or strain. From such stress-induced Raman band shifts, the point-to-point variation of axial fibre stress or strain along an individual fibre in an epoxy matrix can be determined. An example is given of the use of the technique to map the distributions of axial fibre strain in a Nicalon/epoxy fragmentation test specimen and to model the failure processes at the fibre/matrix interface.

Micromechanical Behavior of Carbon Nanotube-Covered SiC Fibers in Polymer Matrix Composites

“…The shift of the E 2g peak is seen to be around 3 cm per percent applied strain for SiC. The E 2g peak shifts of these SiC fibers as a function of applied strain have not yet been reported in the literature, but these results are consistent in order of magnitude with the curves reported for other peak shifts in SiC [11] and carbon [12][13][14] fibers. Increasing the count time during measurement, or the dwell time prior to measurement, did not change these values, implying that beam heating was not an issue.…”

“…Using MRS, the local fiber strain profile within the composites can be obtained by measuring this peak shift. ISS measurements of carbon and SiC fiber composites have been made using MRS, as the Raman peaks are observed to shift linearly to lower wavenumbers under tensile strains and to higher wavenumbers under compressive strains [9][10][11][12][13][14]. Typical results showed some degreee of yield or debonding near the break, with perfect bonding rarely achieved: …”

Direct measurement of fiber bridging in notched glass-ceramic-matrix composites

“…The crystal structure of the silicon carbide NLM202 fiber consists of free carbon nanoprecipitates and nanocrystalline ␤-SiC grains forming an amorphous oxycarbide of chemical formula SiC 1.15 O 0.85 . 19,20 While oxygen is introduced during fiber curing, 21 the existence of excess carbon relative to silicon (attributed to the high C-to-Si ratio in the polycarbosilane precursor) is responsible for the appearance of the prominent 1350 and 1675 cm −1 bands in the Raman spectrum of the SiC NLM202 fiber. These bands correspond, respectively, to the 〈 1g breathing mode and E 2g stretching mode of the C-C bond in the graphite crystal (Fig.…”