Texture Development in Silicon Nitride–Silicon Oxynitride In Situ Composites via Superplastic Deformation

Silicon nitride–silicon oxynitride (Si₃N₄–Si₂N₂O) in situ composites have been fabricated via either the annealing or the superplastic deformation of sintered Si₃N₄ that has been doped with a silica-containing additive. In this study, quantitative texture measurements, including pole figures and X-ray diffraction patterns, are used in conjunction with scanning electron microscopy and transmission electron microscopy techniques to examine the degree of preferred orientation and texture-development mechanisms in these materials. The results indicate that (i) only superplastic deformation can produce strong textures in the β-Si₃N₄ matrix, as well as Si₂N₂O grains that are formed in situ ; (ii) texture development in the β-Si₃N₄ matrix mainly results from grain rotation via grain-boundary sliding; and (iii) for Si₂N₂O, a very strong strain-dependent texture occurs in two stages, namely, preferred nucleation and anisotropic grain growth.