Beryllium is one of the candidate plasma facing materials for use in thermonuclear fusion reactors. The successful joining of beryllium to a copper alloy heat sink requires management of both mechanical and metallurgical issues. Specifically, the direct bonding of beryllium to high-strength copper alloys at elevated temperatures will result in both the formation of deleterious intermetallic compounds at the bond line and, upon cooling to ambient temperatures, the generation of substantial residual stresses due to the large difference in coefficient of thermal expansion between the two materials. Additionally, beryllium components require careful handling to prevent the formation of a tenacious surface oxide which subsequently inhibits metallurgical bonding. In this paper, we review the results of efforts which addressed both metallurgical and mechanical concerns through the utilization of bonding processes which incorporate a ductile layer situated between the beryllium armor and a copper substrate.

Aluminum is one of the few elements which does not form intermetallic compounds with beryllium. Previously reported results have confirmed the viability of brazing beryllium to a thin aluminum layer which had been explosion bonded to a copper alloy substrate. The use of a thin titanium diffusion barrier (between the copper and aluminum) has been shown to prevent undesirable chemical reactions between the copper and aluminum alloys, and remains stable at temperatures approaching the melting point of aluminum. Subsequent work, reported here, has shown that an aluminum-silicon braze alloy can be used to join S-65C beryllium to the aluminum surface of an explosion bonded aluminum/titanium/copper plate to produce a structure which has reasonable integrity at temperatures of 20 and 300 degrees C. Bond specimens possess joint strengths comparable to that of the weakest material; the aluminum layer, but exhibit considerable ductility.

The substitution of a thin layer of AlBeMet 150(registered trade-mark) (a beryllium alloy containing approximately 45 w/o aluminum) for aluminum in the explosion bonded configuration provides the potential for improved bond strength with no loss in chemical stability. Mechanical test results confirmed a substantial strength improvement compared to the aluminum layer specimens.

High heat flux testing in Sandia's Electron Beam Test system (EBTS) has demonstrated the capability of specimens, fabricated using both bonding processes, to withstand a heat flux of 5MW/m² and higher without sustaining damage to the beryllium tiles.

*Work supported by the U.S. Department of Energy under Contract DE-AC04-94AL85000.