ALUMINUM-ASSISTED JOINING OF BERYLLIUM TO COPPER FOR FUSION APPLICATIONS

Five different brazing techniques were evaluated in the process of joi ning beryllium to copper. Aluminum-based filler metals were used in co njunction with aluminum coatings on both beryllium and copper substrat es. This innovative approach was born out of the necessity to inhibit the formation of oxides and intermetallics on the aluminum and berylli um surfaces both before and during the joining process. Several bondin g techniques, diffusion barriers, and oxide inhibitors were employed t o reduce the bonding problem to that of joining aluminum to aluminum. The volume of aluminum in the joint was found to be an important facto r in reducing the segregation of secondary alloying elements at the be ryllium interface. Plasma sprayed aluminum coatings were too porous to use in the as-sprayed condition and were further processed using a ho t isostatic press (HIP) to accomplish full density. The use of plasma sprayed aluminum coatings, Al-12%Si filler metal (Alloy 718), and the HIP process produced excellent bonds between the aluminum coated beryl lium and 1100-Al alloy plate which was explosively bonded to a copper alloy. Bond strengths were measured at 100% of the strength of the 110 0-Al plate strength (90 MPa). The ductility of the aluminum bond was s ufficient to produce extensive necking prior to fracture. (C) 1997 Els evier Science S.A.