Evaluation of Cu as an interlayer in Be/F82H diffusion bonds for ITER TBM

Copper has been investigated as a potential interlayer material for diffusion bonds between beryllium and Reduced Activation Ferritic/Martensitic (RAFM) steel. Utilizing Hot Isostatic Pressing (HIP), copper was directly bonded to a RAFM steel, F82H, at 650°C, 700°C, 750°C, 800°C and 850°C, under 103MPa for 2h. Interdiffusion across the bonded interface was limited to 1μm or less, even at the highest HIP’ing temperature. Through mechanical testing it was found that samples HIP’ed at 750°C and above remain bonded up to 211MPa under tensile loading, at which point ductile failure occurred in the bulk copper. As titanium will be used as a barrier layer to prevent the formation of brittle Be/Cu intermetallics, additional annealing studies were performed on copper samples coated with a titanium thin film to study Ti/Cu interdiffusion characteristics. Samples were heated to temperatures between 650°C and 850°C for 2h in order to mimic the range of likely HIP temperatures. A correlation was drawn between HIP temperature and diffusion depth for use in determining the minimum Ti film thickness necessary to block diffusion in the Be/F82H joint.