Joining Carbon-Carbon Composites and High-Temperature Materials with High-Energy Electron Beams

The use of high energy (E ~ 1-5 MeV) electron beams (HEEB) at high average power (P ~ 50 kW - 1 MW) allows carbon-carbon (CC) composite components to be joined together and bonded to high-temperature metallic materials. HEEB joining utilizes deep-penetration volumetric heating to melt a thin, high-Z braze alloy interlayer. The localized power deposition raises the CC and braze temperatures only at the joint, permitting wetting and reliable joint formation. Traditional joining methods such as furnace brazing and mechanical techniques are not acceptable for production of CC thermal shields or CC-containing tubes for rocket exhaust applications. HEEB joining minimizes thermal expansion failure which can occur with furnace brazing and replaces ad-hoc joining. Science Research Laboratory (SRL) has developed a new generation of pulsed induction linear accelerators which allow reliable, cost efficient production of high average power electron beams with the necessary parameters for CC joining. A unique feature of these accelerators is the high repetition rate (>5000 pps) all-solid-state pulsed power drivers which make these accelerators scalable to MW power levels at an electron beam cost of less than $2/Watt. The induction accelerator technology developed by SRL is consistent with the power densities (300-3000 W/cm2) and beam energies (1-5 MeV) required for CC joining. A HEEB CC joining system based on this technology is described. Preliminary experiments in Phase I will demonstrate HEEB joining and determine joint reliability and strength. Process optimization and the fabrication of thin-walled tubes containing CC-refractory metal bonds are planned for Phase II.