Ultra Sharp Fiber Architectures for Ceramic Composites

Future hypersonic vehicles will be required to fly extended, long term trajectories where the bodies must exhibit high lift-to-drag (L/D) ratios. The need for reduced drag means that the nosetips and leading edges must have small radii, shallow wedge angles, and be erosion resistant. Desirable dimensions include a nose radius on the order of 0.040 inch and a wedge half angle of about 3. This radius is an order of magnitude finer than the existing state of the art. Existing carbon-carbons and ceramic matrix composites (CMCs) made with commercial carbon yarns (2K and 3K tows) result in nosetips and leading edges with radii of 0.5 inch or greater. Fine radii also create operational problems because aerodynamic heat loads increase as the radius decreases. This means that high L/D nosetips and leading edges will be exposed to high temperatures in an oxidizing environment for long periods of time. Thus in order to maintain a sharp radius the nosetips and leading edges must be erosion resistant and able to withstand significant thermal stresses. Thus the problem is to develop low erosion, thermal stress resistant ceramic matrix composites at a geometric scale that is an order of magnitude finer than the existing state of the art.In order to solve this problem Materials Research & Design (MR&D) proposes to develop fine braided tungsten (W) wire CMCs that meet the goals for fine geometry, low erosion, and thermal stress resistance. The proposed effort builds upon past successful collaborations between MR&D and two other businesses. Specifically DE Technologies (DET) and MR&D have designed, analyzed, developed and demonstrated high strength tungsten reinforced braided composites for severe impact applications. Additionally MR&D has supported Exothermics in the development of manufacturing methods to densify chopped W/HfN composites for high temperature erosion resistant CMCs. The proposed Phase II program will bring this team together to design, analyze, fabricate, and characterize fine braided W/HfN CMC leading edges. MR&D will manage the program, analyze the response of the CMC to a hypersonic trajectory, and design braid architectures that will survive the conditions. DET will braid both representative leading edge preforms and additional preforms for densification and characterization. Exothermics will densify the braided tungsten preforms using their process of hafnium slurry infiltration followed by nitridation and HIPping. Braided W/HfN billets will be characterized at SoRI for critical material properties including thermal conductivity, thermal expansion, and high temperature strength.