Abnormal grain growth in iron-containing SiC fibers

Understanding the role of sintering aids during microstructure evolution is critical to the manufacture of densified SiC fibers. A variety of TEM characterization techniques are combined to investigate grain growth behavior in iron-doped SiC fibers. Ultra-large SiC grains in micron size, as the self-assembly of nano sub-grains into a similar orientation, were consistently discovered at the surface and indicative of abnormal grain growth. The growth front consisted of polycrystalline nanograins wetted by iron-rich particles, where several sub-grains were found to unify their (111) planes with a misorientation angle less than 10°, indicating grain rotation at the growth front. It is proposed that iron-rich particles form a quasi-liquid interfacial phase during sintering, which facilitates coherent attachment of grains and results in fast grain growth using neighboring irregular-shaped nanograins as building blocks. The imperfect ordered coalescence of nanograins introduces structural heterogeneities, including low angle grain boundaries and porosities.