Improved Fracture Toughness and Oxidation Resistance in Small, Composite, Liquid-Rocket Combustion Chambers

In previous work, Ultramet has demonstrated an innovative variation of chemical vapor infiltration (CVI) in which two or more carbide coatings are applied in fine, alternating layers. The interfaces between these layers act as highly effective toughening mechanisms by inhibiting crack propagation. The first application involved the deposition of a layered HfC/SiC coating on carbon/carbon (C/C) and diboride matrix composites, which has been shown to provide oxidation resistance in the 1600-2500@C range. A second coating, which provided improved glass forming/crack sealing capability for cyclic use at lower temperatures, was developed based upon a layered Si3N4/SiC system. In this Phase I program, Ultramet proposes to demonstrate the feasibility of a highly innovative approach for the fabrication of tough, reliable carbon fiber/carbide matrix composite combustion chambers, in which a layered carbide matrix material will be applied to a carbon fiber preform by CVI. Current ceramic matrix composites, such as C/SiC, are limited by the fracture toughness of the SiC matrix, leading to exposure and degradation of the high-strength carbon fiber reinforcements, while SiC/SiC composites are limited by the maximum use temperature of the SiC fibers. The ability to maintain the structural integrity of combustion chambers for longer durations, at potentially higher temperatures, will provide substantial engine performance improvements. Ultramet will team with C-CAT, a leading C/C manufacturer, and Rocketdyne, which will provide hot-fire testing and technical assistance.