BERYLLIUM-COPPER REACTIVITY IN AN ITER JOINING ENVIRONMENT

Beryllium-copper reactivity was studied using test parameters being co nsidered for use in the ITER reactor. In this application, beryllium-c opper tiles are produced using a low-temperature copper-copper diffusi on bonding technique. Beryllium is joined to copper by first plating t he beryllium with copper followed by diffusion bonding the electrodepo sited (ED) copper to a wrought copper alloy (CuNiBe) at 450 degrees C, 1-3 h using a hot isostatic press (HIP). In this bonded assembly, ber yllium is the armor material and the CuNiBe alloy is the heat sink mat erial. Interface temperatures in service are not expected to exceed 35 0 degrees C. For this study, an ED copper-beryllium interface was subj ected to diffusion bonding temperatures and times to study the reactio n products. Beryllium-copper assemblies were subjected to 350, 450 and 550 degrees C for times up to 200 h. Both BeCu and Be2Cu intermetalli c phases were detected using scanning electron microscopy and quantita tive microprobe analysis. Growth rates were determined experimentally for each phase and activation energies for formation were calculated. The activation energies were 66 mol and 62 kJ mol(-1) for the BeCu and Be2Cu, respectively. Tensile bars were produced from assemblies consi sting of coated beryllium (both sides) sandwiched between two blocks o f Hycon-3. Tensile tests were conducted to evaluate the influence of t hese intermetallics on the bond strength. Failure occurred at the bery llium-copper interface at fracture strengths greater than 300 MPa for the room-temperature tests. At 300 degrees C, the fracture strength wa s decreased significantly and, in contrast to the room-temperature tes ts, the fracture initiated in the copper-copper bond. The change in fr acture initiation is attributed to a decrease in the residual stresses at the beryllium-copper interface at the higher temperatures and a de crease in the intrinsic fracture strength of the ED copper. (C) 1998 P ublished by Elsevier Science S.A. All rights reserved.