CVD deposition of highly Al-rich mullite coatings

摘要

Functionally graded mullite (3Al_2O_3·2SiO_2) coatings have been grown for Si-based substrates and the composition has been tailored in these coatings, with the Al/Si ratio being stoichiometric (～ 3) at the coating/substrate interface for coefficient of thermal expansion (CTE) match, and increasing monotonically towards the outer coating surface. These functionally graded coatings were found to have the highest Al-rich mullite reported to date. At these extremely high Al/Si ratios, mullite structure breaks down and the formation of a nano-sized high-alumina rich phase occurs. High-resolution transmission electron microscopy has been used to characterize the structure and composition of high alumina mullite.