THE INTEGRITY EVALUATION OF THE WELD JOINT OF SPHERICAL ROCKET MOTOR CASE

Abstract The Institute of Space and Astronautical Science (ISAS) is undertaking the launching of spacecraft for space observations and interplanetary explorations. The spherical rocket motor case of satellite launchers was made of Ti-6A1-4V alloy, however, to reduce the weight and fabrication cost, the material of the case was changed to Ti-15V-3Cr-3Sn-3AI alloy because of its good cold formability and the high strength. However, it was found that the hardness of weld joint was higher than that of base metal and the fracture toughness was lower when heat treated by a conventional aging process. This report describes the development of a new heat treatment process to obtain the high strength of base metal and the high fracture toughness of the weld joint, and the evaluation of the integrity of the weld joint by acoustic emission and radiography. The developed heat treatment process is as follows: after solution treatment, the motor case was aged at a relatively low temperature (preaging), welded, and then ...