Ultra-Refractory Composites for Propulsion Applications

This phase I research proposes an efficient approach to develop a reliable chemical vapor infiltration (CVI) process for HfB2-HfC-SiC matrices for carbon fiber composites and chemical vapor deposition (CVD) processes for depositing coatings for the same compositions, and; second, to design, fabricate, and evaluate ultra-refractory CMCs consisting of a carbon fiber reinforcement reinforcing a functionally graded matrix of HfB2-HfC-SiC graded to SiC. These advanced, lightweight materials are likely enabling for future propulsion goals. The HfB2-HfC-SiC monolithic material has been shown to exhibit high temperature performance superior to all other materials tested under reentry conditions. The oxidation layer formed on these monolithic compositions was extremely tenacious, displaying no spallation after cooling from 2200ºC. It is thought that if deposited as the matrix of a carbon fiber reinforced ceramic matrix composite, the oxide layer will prevent the ingress of species that will degrade the interfacial debond layer and the carbon fiber, allowing for the retention of mechanical properties under extreme temperatures and oxidizing environments. Thermodynamic modeling will allow for efficient optimization of the deposition conditions; High temperature oxidation testing of the fabricated composites at 4500ºF will provide needed feedback to improve the design for the Phase II work.