Microstructure characterization of oxide coatings deposited by pulsed excimer laser ablation

This work addresses the issues of coating of oxide fibers or laminates with debondable oxide interphases. It fabricates a model system for an alumina matrix reinforced with alumina fibers, wherein an enstatite interphase is transformation weakened, resulting in interphase debonding. A suitable multilayer coating sequence was chosen to act as a chemical bridge between the alumina fiber and matrix. The pulsed excimer laser ablation method (KrF excimer laser of λ = 248 nm) was used to deposit several oxide materials individually onto silicon wafers. Titania (TiO₂ or T), aluminum titanate (Al₂O₃ · TiO₂, Al₂TiO₅ or AT), and enstatite (MgO · SiO₂, MgSiO₃ or EN) layers were deposited from sintered target materials. X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy investigations indicated that as-deposited coatings were amorphous or partially crystallized into nanosize grains, and their thicknesses were uniformly distributed over the Si-substrate, growing in columnar texture (although not as pronounced for enstatite). Transmission electron microscopy/energy dispersive spectroscopy analysis confirmed that the chemical composition of the coating materials was the same as that of the target materials and that the coatings were completely crystallized into nano- or submicrometer grain size after annealing at 1200°C for 1 h. With these data, sapphire monofilaments were sequentially coated with five layers of Al₂TiO₅, TiO₂, MgSiO₃, TiO₂, and Al₂TiO₅. This construction provided a chemical bridge between the alumina monofilament and the enstatite debondable interphase.