Increased Component Size of Cf/ZrC CMCs for Hypersonic and Related Applications, Phase II

Hypersonic weapon flight performance is improved significantly by the drag reduction achieved when thermal protection system (TPS)-related structures remain sharp and shape-stable under all flight conditions. Ultramet’s approach to this design goal is to utilize its carbon fiber-reinforced zirconium carbide (Cf/ZrC) ceramic matrix composite (CMC) material for these applications. Ultramet has developed and established the feasibility of the Cf/ZrC CMC material for hypersonic and other reentry applications through more than 20 years of development, characterization, and testing in relevant environments, during which Cf/ZrC has shown great promise in these types of applications. The proposed project will build upon successful scaling of Cf/ZrC CMC production capacity underway in ongoing work in order to accelerate material adoption, complementing concurrent work while addressing issues that could not be pursued within the scope of those efforts. The scale of fiber preform and matrix melt infiltration processing capabilities will be increased, with a doubling of the capacity of the melt infiltration process, in order to make larger component sizes available to the end user. The resultant larger-scale CMC billets will be characterized mechanically and thermally. This project also seeks to improve material models for the Cf/ZrC CMC. Current models are linear-elastic and are overly conservative. Material performance in operating environment testing at the component level has not mirrored the component performance predicted by the models, which tend to predict component failure when in reality failure does not occur. Destructive analysis of the CMC material will be performed after exposure to heating loads representative of high-speed flight to visualize non-linear behavior such as damage and plasticity and collect residual mechanical properties of the Cf/ZrC CMC. The results will be compared with the properties of the baseline untested material, and incorporated into the modeling effort so that a more non-linear model can be developed whose predictions better correlate with actual material performance. Finally, optimization of elevated temperature mechanical testing will be explored. The Cf/ZrC CMC material is susceptible to pesting oxidation at lower temperatures, and traditional mechanical testing at elevated temperatures involves long, slow heating to temperature in environments containing non-negligible amounts of oxygen. The result is pesting oxidation and a non-representative reduction in material properties. Mechanical testing optimization will include rapid heating to prevent specimen damage. The material properties generated will be compared with the baseline to ascertain the level of improvement obtained. The ultimate goal of the characterization efforts is to improve the Cf/ZrC CMC material models for use by system designers, enhancing their confidence in using the material and enabling acceleration of material adoption by the end user.