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 envisaged next-step machines, relies on the use of junctions for coupling the armour materials to the heat sink and cooling tubes. A suitable diffusion bonding process for manufacturing the high heat flux components of ITER have been developed. The process parameters for defining the bonding technology are reported. The dependence of the load applied on the sample, the bonding temperature, dwell time and surface preparation were studied and the results applied in the construction of the mockups. Results of the shear tests performed to define the process parameters 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 activated beryllium surface. This electrolytic deposition method gave good results and reproducibility so it was decided to use copper as interlayer in order to obtain a silver-free joint. After selecting the best process, medium-scale mockups of high heat flux components for testing on the electron beam facility were manufactured. The actively cooled mockups 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 mockups have been submitted to ultrasonic inspection to detect bonding defects.