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Thursday, June 5, 2008 - 9:45 AM

High Strength Diffusion Bonding of Beryllium to CuCrZr for ITER Applications

J. D. Puskar, Sandia National Laboratories, Albuquerque, NM; S. H. Goods, C. H. Cadden, Sandia National Laboratories, Livermore, CA

The ITER experimental fusion reactor requires that S-65C beryllium be joined to an underlying precipitation-strengthened copper heat sink alloy (C18150) that is also bonded to a 316L stainless steel structure.  Diffusion bonding using hot isostatic pressing (HIP) has been identified as the best joining option given the numerous engineering and material requirements.  Specifically, the joining process between the beryllium tiles and copper alloy must be done at as low of a temperature as possible to minimize overaging of the copper alloy.  In this study, various materials and processing conditions have been studied to determine their effects on the resulting strength of the joints. 

Various metallic interlayers and combinations thereof were investigated for their ability to promote bonding, prevent oxidation and provide compliancy. Within this matrix, beryllium tiles were prepared with different surface finishes to determine the effects of roughness on bond strength.  Titanium interlayers were successful in preventing the formation of deleterious Be-Cu intermetallics.  Several forms of titanium and copper interlayers were evaluated, including sputter deposition, electron beam evaporation and free standing Cu foils.

Bond strength measurements were quantified using a modified ASTM A263 shear test. Using shear strength as the primary metric for bonding integrity, the most promising combinations of interlayers were investigated while varying the HIP parameters.  The results suggest that bonding temperatures of 580 and 560C provide the maximum achievable bond strength, evidenced by fracture in the beryllium tile as opposed to along the joint.  Joint strength is significant, even at temperatures as low as 540C

Lastly, the joint microstructures have been analyzed using several different analytic techniques including optical and electron microscopy as well as microprobe and Auger electron spectroscopy to determine diffusion profiles and intermetallic formation.  These results will be discussed as they relate to the relative bond strengths that have been measured.


Summary: Low temperature diffusion bonding of beryllium to CuCrZr was investigated for fusion reactor applications. Hot isostatic pressing was accomplished using various metallic interlayers. Diffusion profiles suggest that titanium is effective at preventing Be-Cu intermetallics. Shear strength measurements suggest that acceptable results were obtained at temperatures as low as 540C.