Optimization of condition for invar/stainless HIP diffusion bonding

Wakui, Takashi  ; Naoe, Takashi   ; Kogawa, Hiroyuki  ; Haga, Katsuhiro  ; Wakai, Eiichi  ; Takada, Hiroshi   ; Futakawa, Masatoshi  

The mercury target vessel has large size as 1.31.32.5 m. In view of reducing the amount of wastes, we have studied the structure so that the fore part could be separated. The flange is required to have high seal performance less than 110 Pam/s. Invar with low thermal expansion is a candidate. Due to its low stiffness, however, the flange may deform when it is fastened by bolts. Practically invar is reinforced with stainless steel where all interface between them has to be bonded completely with the HIP bonding. In this study, we made specimens at four temperatures of 973, 1173, 1373 and 1473 K and conducted tensile tests. The specimen bonded at 973 K had little diffusion layer, and so fractured at the interface. The tensile strength reduced with increasing the temperature, and the reduced amount was about 10 % at 1473 K. The analyzed residual stresses near the interface increased by 50 % at maximum. Then, we concluded that the optimum temperature was 1173 K.