QUANTITATIVE DETERMINATION OF THE MISORIENTATION DEGREE OF PYROCARSONS

摘要

The orientation angle (OA), corresponding to the full-width at the half maximum (FWHM) intensity of the opening angle of the arc of (002) reflections, displays an important role for the quantitative evaluation of pyrocarbon textures. In this study, a quantitative method for determining the misorientation degree of pyrocarbons was proposed based on the high resolution transmission electron microscopy (HRTEM) and the selected area electron diffraction (SAED) by the computer-aided image analysis. Fast Fourier transform (FFT) of the HRTEM image was performed to obtain the diffractogram of the pyrocarbon layers in the reciprocal space. The gray centroid method and the scanning algorithm with a polar axis were applied to extract the azimuthal intensity maxima of the ring (002) reflections. OA was obtained by an improved Gaussian function with a direct component fitting the intensity data versus the azimuth angle. The FFT can be avoided when measuring OA from the SAED pattern. The accuracy of the algorithm has been approved by measuring the SAED images in some research work reported by others. The system has been applied to the quantitative texture characterization of pyrocarbon matrix of carbon/carbon composites fabricated by CVI, and the misorientation degree has been appraised at a higher precision compared to the polarized light microscopy (PLM).