TECHNOLOGIES OF JOINING BETWEEN ITER REFERENCE GRADE BERYLLIUM AND COPPER-ALLOYS BY DIFFUSION BONDING PROCESS

The design of plasma-facing components for ITER, as for any of the env isaged next-step machines, relies on the use of junctions for coupling the armour materials to the heat sink and cooling tubes. A suitable d iffusion bonding process for manufacturing the high heat flux componen ts of ITER have been developed. The process parameters for defining th e bonding technology are reported. The dependence of the load applied on the sample, the bonding temperature, dwell time and surface prepara tion were studied and the results applied in the construction of the m ockups. Results of the shear tests performed to define the process par ameters for different heat sink materials, such as CuCrZr alloy and DS copper, are reported. The S65 beryllium grade used (supplied by Brush and Wellman) had cubic and castellated finishing to increase its high heat flux resistance. A shear strength of about 150 MPa was obtained by using an interlayer of electrolytic copper deposited on the activat ed beryllium surface. This electrolytic deposition method gave good re sults and reproducibility so it was decided to use copper as interlaye r in order to obtain a silver-free joint. After selecting the best pro cess, medium-scale mockups of high heat flux components for testing on the electron beam facility were manufactured. The actively cooled moc kups had a 50x30x8mm beryllium armour (castellated and non-castellated ), with two kinds of heat sink material (Glidcop Al25 and CuCrZr alloy ). Both the samples produced for the shear tests as well as the mockup s have been submitted to ultrasonic inspection to detect bonding defec ts.