SOLID-STATE BONDING OF BERYLLIUM TO COPPER AND VANADIUM USING TRANSITION LAYERS

Beryllium is a material under consideration for divertor surfaces in t he international thermonuclear experimental reactor (ITER). Since Be i tself is not a suitable structural material for constructing the diver tor, it needs to be bonded to other materials with sufficiently high t hermal conductivity, which at the same time satisfy structural require ments such as adequate strength and fracture toughness. Bonding of Be to other materials is usually accompanied by (a) mismatches in thermal expansion and/or (b) metallurgical incompatibilities. In an attempt t o minimize the thermal expansion mismatch we employed Fe or Ni transit ion layers for the bonding of Be to a copper alloy by hot isostatic pr essing. To alleviate the thermodynamic incompatibility between Be and most other metals, thin Ag foil (130 mu m) was used as a reaction barr ier. Other experiments involved bonding Be (via an Ag reaction barrier ) to a V-5Cr-5Ti (wt%) alloy. An Al-Be transition layer for bonding Be to a copper alloy was also explored. The microstructures of the inter faces were examined by optical and scanning electron microscopy. Shear tests carried out with Cu/Fe/Ag/Be and V/Ag/Be specimens indicated av erage room temperature shear strengths of 52 and 78 MPa, respectively. Fracture occurred usually at the Ag/Be interfaces, which were therefo re the weakest link in the bonded specimens. (C) 1997 Elsevier Science B.V.