A thruster functions as a small engine for orbit maneuver and attitude control of a satellite. While conventional bipropellant thrusters are mainly made of Nb alloy, a Si3N4–ceramics thruster was successfully developed and used in Venus explorer AKATSUKI by ISAS/JAXA. Now, for further size enlargement targeting future interplanetary missions, ISAS/JAXA is currently developing a metal/ceramics hybrid thruster: heat-resistant Si3N4 is used only in the high-temperature sections (combustion chamber and throat), whereas light-weight Ti-6Al-4V alloy sheet is used in the low-temperature section (nozzle skirt) of the thruster. Robust dissimilar joining of active metal of Ti-6Al-4V alloy to ceramics of Si3N4 is the key technology for the hybrid thruster, and it requires promoting residual-stress relaxation and suppressing brittle intermetallic compounds formation by insertion of Nb-interlayer. It has been achieved through transient-liquid-phase bonding (TLPB) of Ti-6Al-4V/Nb side with Cu and Ni laminated filler prior to active-metal brazing of Nb/ Si3N4 side with Ti-added Ag-Cu based CUSIL-ABA filler or Ti-added Ag-based SILVER-ABA filler. This two-step bonding brought about joints fractured from inside of Si3N4 and achieved higher average strength. The effectiveness of stress-accommodation via Nb interlayer and filler’s plastic flow was quantitatively verified with reasonable fidelity by finite-element analysis incorporating temperature-dependent elasto-plastic properties. Professor, Institute of Space and Astronautical Science, JAXA, Japan Abstract Multi-material Designed Satellite Thruster through Ceramics/metal Dissimilar Joining Session 2 ｜After graduating the University of Tokyo in 1985, Eiichi Sato has been working for ISAS/JAXA, specializing high temperature deformation and superplasticity, in addition to structural materials and reliability for space engineering. He is now serving Program Director of ISAS space science projects. NIMS Award Symposium 2023 High-temperature MaterialsEiichi Sato Invited Talk S2-1 29
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