Effectiveness of Monazite Coatings in Oxide/Oxide Composites after Long-Term Exposure at High Temperature

• Published in: Journal of the American Ceramic Society Vol. 86; no. 2; pp. 325 - 332
• Main Authors: Keller, Kristin A., Mah, Tai-Il, Parthasarathy, Triplicane A., Boakye, Emmanuel E., Mogilevsky, Pavel, Cinibulk, Michael K.
• Format: Journal Article
• Language: English
• Published: Westerville, Ohio American Ceramics Society 01.02.2003; Blackwell; Wiley Subscription Services, Inc
• Subjects: Applied sciences; Building materials. Ceramics. Glasses; Ceramic industries; Chemical industry and chemicals; coatings; composites; Exact sciences and technology; oxides; Structural ceramics; Technical ceramics; Calcium Phosphates; Long term test; Monazite; Coated fiber; Fiber reinforced material; Fracture surface; High temperature; Experimental study; Microstructure; Oxide ceramics; Composite material
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/j.1151-2916.2003.tb00018.x

The effectiveness of monazite (LaPO4) in providing an oxidation‐resistant weak fiber/matrix interface was evaluated in a fiber roving/thin coating/ceramic‐matrix composite with >20% fiber volume fraction. Nextel™ 610/monazite/alumina composites were fabricated and tensile tested after isothermal exposures of up to 1000 h. Some strength loss was seen after short‐term exposures (1100°–1200°C/5–250 h); however, no further loss was observed after 1000 h at 1200°C. Conversely, control samples containing uncoated fiber displayed >70% strength losses after only 5 h at 1200°C. Fiber pullout was seen in monazite‐containing samples even after 1000 h at 1200°C. Debonding was predominantly in the coating or at either the fiber/coating or coating/matrix interface. Push‐out testing confirmed the weakness of the monazite coating interface.