High-resolution Parallel-beam Powder Diffraction Measurement of Sub-surface Damage in Alumina-silicon Carbide Nanocomposite

The sub-surface damage in ground and subsequently annealed alumina/silicon carbide nanocomposite has been studied by analysis of the x-ray diffraction line width as a function of incidence angle. Bragg peak broadening fell as the depth of penetration of the x-ray beam increased. Despite substantial anisotropy in the uniform compressional strain in the surface of the ground material, no significant azimuthal anisotropy was found in the peak widths. The surface extrapolated broadening decreased by an order of magnitude on annealing but the rate of fa ll of broadening with depth did not change. No such changes were observed on annealing polished material. Williamson-Hall analysis of the annealed ground material showed an order of magnitude decrease in the diffracting domain size at the surface compared with that of the bulk material, where the diffracting domain size was of the order of the grain size.