Low-Cost C/SiC Liquid Propulsion Rocket Nozzles via Rapid, Forced Flow CVI

Liquid rocket engine systems currently in development or being considered for future development will require a variety of liquid propulsion subsystems for axial, reaction control, target intercept, and auxiliary propulsion. Many of these proposed systems are critically dependent on the development of advanced high-temperature materials for specific propulsion sub-systems. Thrust chambers/nozzles currently being produced are typically fabricated from various refractory metals and refractory metal alloys. Although refractory metal materials have proved to be highly reliable, they are extremely weight-inefficient due to their high density and low specific mechanical properties. Recent developments in light-weight, high-temperature ceramic-matrix composites (CMCs) offer promise to increase both performance and efficiency over currently available propulsion materials. Current state-of the-art CMCs are being fabricated by methods of conventional chemical vapor infiltration (CVI). Conventional, isothermal/isobaric CVI techniques require intentionally slow deposition rates in order to uniformly infiltrate and densify the continuous fiber preforms while minimizing through-the-thickness density gradients. These slow CVI densification processes routinely require 300-400 hours to complete, resulting in very long product lead times and thus relatively high product cost. The objective of this Phase I program is to develop and evaluate an innovative forced flow CVI process for the rapid densification of carbon fiber-reinforced silicon carbide-matrix (C/SiC) composite rocket nozzles. The goal of this development is to successfully reduce the densification cycle by at least 75%, resulting in a composite nozzle fabrication cost reduction of over 50%. Triaxially braided, multilayer carbon fiber performs will be fabricated over geometrically contoured mandrels and rapidly densified with SiC using an economical forced flow CVI technique. Process conditions will be established for densifying the nozzle components to a minimum target density of 2.3 gm/cm3 (88% theoretical) inless than 100 hours. Tubular composite test specimens, representative of both the combustion chamber and th