Double Interface Coatings on Silicon Carbide Fibers
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Double Interface Coatings on Silicon Carbide Fibers Jun C. Nable1, Shaneela Nosheen1, Steven L. Suib1,2*, Francis S. Galasso1, Michael A. Kmetz3 University of Connecticut, Department of Chemistry, Storrs, CT 06269 2 University of Connecticut, Institute of Materials Science, CT 06269 3 Pratt & Whitney, East Hartford, CT 1
* Corresponding author Abstract Interface coatings on fibers are important in ceramic matrix composites. In addition to providing toughness, the interface coating must also protect the reinforcing ceramic fibers from corrosive degradation. A double interface coating has been applied onto silicon carbide fibers. The double interface coating is comprised of a combination of nitride and oxide coatings. Among the nitrides, boron nitride and titanium nitride were utilized. These nitrides were deposited by CVD. The metal oxides of choice were aluminum oxide and zirconium oxide which were applied onto the nitride coatings by MOCVD. The phases on the coated fibers were determined by XRD. The surface coating microstructures were observed by SEM. The effect of the coatings on the tensile strengths was determined by Instron tensile strength measurements. Introduction Ceramic matrix composites (CMCs) are widely utilized as high temperature application components. Ceramics are chosen due to their resistance to corrosion and to chemical deterioration at elevated temperatures. Common applications of CMCs include automobile and aircraft parts and components [1]. Ceramic fiber reinforcements such as SiC are typically embedded in a ceramic matrix by high temperature processes. These composites may be fabricated by chemical infiltration, hot pressing, and liquid phase sintering. However, a major issue encountered during this high temperature fabrication step, as well as during high temperature operation is the exposure of the reinforcing fiber material to corrosive conditions and material interdiffusion resulting in a decrease in the overall mechanical strength of the composite eventually leading to failure of the entire component. Such degradation can be minimized by providing an interfacial barrier coating between the fiber reinforcement and matrix material to prevent interdiffusion of materials and exposure to oxidative damage. Interface coatings such as BN and C are ideal materials to provide toughness in ceramic matrix composites however they are prone to oxidation in the presence of air at high temperatures [2,3]. Alternative materials include metal oxides, aluminosilicates, monazites and xenotimes [4-6]. Common coating techniques to deposit an interface layer onto ceramic fibers include sol-gel and physical vapor deposition. The sol-gel technique is a wet chemical approach which subsequently requires a high temperature post treatment to densify the coating. Chemical vapor deposition (CVD) is another coating technique that can provide a dense, compact coating in a single deposition step. This method also offers the advantage of not being a line-of-sight deposition method.
T3.11.2
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