ULTRA-THIN 3-D CERAMIC MATRIX COMPOSITE CLADDING

The deployment of ceramic matrix composites (CMCs) to nuclear-related applications, accelerated by the 2011 Fukushima accident through the Congressionally-mandated Accident-Tolerant Fuel (ATF) program administrated by the Department of Energy, still requires several technical advancements to achieve widespread use in nuclear reactor structures and fuel cladding. Silicon carbide, as part of a SiC matrix-SiC fiber system, is recognized as the primary material option to achieve the ATF goals, but the present-day manufacturing format of fibers in twisted tow collections of wound fibers that are then braided or weaved to create the composite reinforcement backbone presents multiple performance issues for nuclear fuel component manufacturers. These performance shortcomings include strength degradation in the SiC fibers due to the damage induced from the weaving process, reduced thermal conductivity due to both the residual porosity in the fiber weaving and layup as well as the strength reduction compensating increase in composite component thickness, and limitations of full matrix formation through chemical vapor infiltration because of the inaccessibility of a significant portion of the residual porosity along with the thicker component dimension. Free Form Fibers (FFF) proposes a new, novel approach to fabricate a non-woven fiber architecture for CMCs using its additive manufacturing-based Rapid Laser-Induced Chemical Vapor Deposition (R-LCVD) technology, which would eliminate the need for fiber weaving and also open an opportunity to create innovative metal matrix composite-ceramic matrix composite (MMC-CMC) hybrid structures. This non-woven design, termed micro trellises, would allow for several important technical advances needed to achieve the DOE and nuclear industry's goal for safe, higher efficiency fuel designs. The non-woven architecture significantly reduces the residual porosity and increases the possible fiber volume fraction loading, while also preventing the strength-reducing fiber-to-fiber interactions. These features minimize the necessary CMC component thickness, providing positive benefits to the bulk thermal conductivity, component weight reduction, and easier and quicker matrix formation via vapor infiltration. The program presented by FFF in this proposal would demonstrate the viability of fabricating the micro trellis design on a coupon-level scale, combining FFF's extensive capabilities to form SiC fiber arrays and trellis-like posts on substrates as well as coat the fibers and posts with interface coating materials. Once the non-woven fiber coupons have been formed, they would subsequently be vapor infiltrated to create a CMC component, or a MMC-CMC component should a metal substrate be used. Component-level properties like thermal conductivity would be evaluated as well as more fundamental mechanical properties of the trellis structures' tensile and adhesion (to the substrate) strengths. The development of FFF's micro trellis fiber design will lead to several needed technical advances for CMC technology, impacting a wide range of applications including the nuclear power, aviation, and aerospace industries. One of the most significant improvements will be the reduction in overall CMC manufacturing economic costs for nuclear fuel reactor components such as cladding.