Aluminum-assisted joining of beryllium to copper for fusion applications

Five different brazing techniques were evaluated in the process of joining beryllium to copper. Aluminum-based filler metals were used in conjunction with aluminum coatings on both beryllium and copper substrates. This innovative approach was born out of the necessity to inhibit the formation of oxides and intermetallics on the aluminum and beryllium surfaces both before and during the joining process. Several bonding techniques, diffusion barriers, and oxide inhibitors were employed to reduce the bonding problem to that of joining aluminum to aluminum. The volume of aluminum in the joint was found to be an important factor in reducing the segregation of secondary alloying elements at the beryllium interface. Plasma sprayed aluminum coatings were too porous to use in the as-sprayed condition and were further processed using a hot 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 beryllium and 1100-Al alloy plate which was explosively bonded to a copper alloy. Bond strengths were measured at 100% of the strength of the 1100-Al plate strength (90 MPa). The ductility of the aluminum bond was sufficient to produce extensive necking prior to fracture.