Precipitation Coating of Rare-Earth Orthophosphates on Woven Ceramic Fibers—Effect of Rare-Earth Cation on Coating Morphology and Coated Fiber Strength
Abstract:Monazite (La, Ce, Nd, and GdPO4) and xenotime (Tb, Dy, and YPO4) coatings were deposited on woven Nextel™ 610 and 720 fibers by heterogeneous precipitation from a rare-earth citrate/phosphoric acid precursor. Coating phases and microstructure were characterized by SEM and TEM, and coated fiber strength was measured after heat treatment at 1200°C for 2 h. Coated fiber strength increased with decreasing ionic radius of the rare-earth cation in the monazite and xenotime coatings, and correlates with the high-temperature weight loss and the densification rate of the coatings. Dense coatings with trapped porosity and high weight loss at a high temperature degrade fiber strength the most. The degradation is consistent with stress corrosion driven by thermal residual stress from coating precursor decomposition products trapped in the coating at a high temperature.
Document Type: Research Article
Publication date: July 1, 2008