Reactive Fusion Welding for Ultra-High Temperature Ceramic Composite Joining

For this Phase I program, MO-SCI Corporation and Missouri University of Science and Technology (Missouri S&T) will develop reactive fusion and reactive plasma welding techniques that are capable of joining ultra-high temperature ceramic (UHTC) composites. Past work at Missouri S&T demonstrated the feasibility of fusion welded UHTC composites. This program will build on the joining successes at Missouri S&T through development of reactive and non-reactive filler materials that are needed to improve weld joint quality. Preheat temperature, power input, filler type, filler introduction rate, and cooling rate will be studied to generate a list of critical process variables that affect the quality of fusion welded joints between UHTC composites. Size and geometry restrictions of 2 welding processes will be assessed to better understand the applicability to the manufacture and repair of integrated TPS. The collaborative efforts will 1) demonstrate the feasibility of low porosity fusion welded UHTC joints, 2) measure the ambient and high temperature mechanical properties for three joint geometries, and 3) quantify the effects of the proposed fusion joining processes on the thermal conductivity of the joints. Joints with predictable thermal and mechanical behavior will be produced at the conclusion of this research and joining of these welded UHTC composites to high temperature metallic alloys will be demonstrated. BENEFIT: Military applications for UHTC fusion welding include repair, fabrication, and fixturing of combustor liners and nozzle divergent seals found on Air Force, Navy, Marine and Army turbine engines. Ceramic armor repair and integration of ceramic armor into military transport vehicles is another potential application for the ceramic welding identified in this work. Ceramic welding will enable armor designs that use ceramic armor tiles as load bearing structures rather than sacrificial or ¡°parasitic¡± components. Weight reduction realized by increased use of lightweight ceramics as structural components will relate to large cost savings associated with reduced fuel consumption. Results from Phase I and Phase II will be used to develop similar joining concepts that will decrease the maintenance cost of other high wear and high temperature, ceramic based components. Commercial applications for the joining solutions outlined in this proposal include repair and remanufacture of large ceramic crucibles designed to contain molten metals and integration of ceramic wear components in large diesel engines. Weldability of HfB2-B4C composites may also enable certain fission reactor designs that require complex shaped neutron shielding. The proposed work in the Phase I program will not only develop welding technologies and methods that are applicable to commercial applications, but it will generate a number of consumable welding products that can be commercialized for use with existing welding systems at ceramic fabrication shops.