11:05 〜 11:30
[14M-PL2] Mechanical Properties and Reliability of Structural Materials for Spacecraft Applications
キーワード：Aerospace, Rocket Engine, Creep- fatigue, Ceramic-metal Hybrid Thruster, Transient liquid phase bonding
Materials used in space vehicles are required to improve their mechanical properties and reliability in extraordinary and/or unique environments in addition to their basic requirements of high specific strength and toughness, especially for propulsion systems. In this talk, low cycle creep-fatigue of combustion chamber for liquid rocket engine and ceramics/metal hybrid thruster for an interplanetary probe are introduced. As LH2/LOX engines can utilize their fuel as coolant, their combustion-chamber is made of Cu alloy with good thermal conduction. In one operation cycle, it exposed to a large temperature cycle, which causes one fatigue cycle reaching to plastic region and including low strain-rate deformation. This creep-fatigue caused through cracking even in 20 combustion cycles. Compared with simple creep and simple fatigue, this creep-fatigue has much shorter rapture life, which is attributed to transient creep deformation appearing in each cycle. As thrusters use storable ambient temperature propellant, its combustion chamber should be heat tolerant. For further deep-space exploration, multi-material hybrid thruster is under developing: Si3N4 is applied for combustion chamber and nozzle skirt is made of Ti-6Al-4V. To braze ceramics to Ti alloy is challenging because of brittle intermetallics formation in addition to difficulty of thermal stress relaxation. Introducing Nb interlayer and applying two-step bonding procedure consisting of TLPB (transient liquid phase bonding) for Ti/Nb first and brazing for Nb/Si3N4 second, sound Ti-6Al-4V/Nb/ Si3N4 bonding is achieved.