Diffusion Bonding of W/ODS Steel using Pure Iron Insert for Fusion Reactor Applications

The combination of tungsten (W) and oxide dispersion strengthened ferritic steel (ODS-FS) is considered to be adequate for the application to fusion diverter components. Joining of the two materials is hence essential to fabricate the required components. However, W cracks easily during the bonding process due to a large difference in the coefficients of thermal expansion (CTE) between these two materials. In this study, we attempted the reduction of the thermal stress using pure iron as an insert material for diffusion bonding of W and ODS-FS. The bonding strength of the bonded specimens was evaluated by four-point bend tests with a specially designed fixture. It was found that the bonding strength significantly depends on the grain structures such as grain size and grain orientation in W used for the W/ODS-FS joint. A much higher strength of the joint was obtained for the W with a relatively fine and equiaxed grain structure than for that with rolled or swaged grain structures.