BW-Electrofusion's diffusion bonding technique employs a combination of temperature and pressure to create the metallurgical joint. Using both of these critical parameters, rather than simply temperature alone, gives diffusion bonded windows their important advantages over conventionally brazed windows.

 

 

While high temperature liquidus brazing may provide brazed window joints of high temperature resistance, it also induces structurally weakening grain growth in the beryllium window material. Since diffusion bonding is accomplished at temperatures below the melting point of the braze alloy, it results in high temperature performance without compromising the strength of the beryllium. By controlling the pressure in the process, diffusion bonding offers control over braze alloy flow, meaning no high absorption alloy material in the active area of the window. Since diffusion bonding is a vacuum furnace process, many assemblies (lots of over 100 units have been brazed successfully) can be processed in one operation, which dramatically lowers the cost for larger quantities. The process also works well with very thin beryllium foil. For example, 0.001" (25µm) thick Be foil has been consistently brazed leak tight, and prototypes with even thinner foils have already been demonstrated.

 

 

Because the braze alloys used in diffusion bonding will diffuse at different rates into various frame materials, BW-Electrofusion can assist you in designing the optimal joint configuration for your frame material or the material combination which best suits your needs. Considerations include: allowing sufficient area to join the beryllium to the frame, known as the "faying" surface, designing the joint for survivability under operating conditions as well as during any subsequent manufacturing operations (such as welding or other joining processes), and choosing the best frame material for thermal and electrical conductivity, as well as thermal expansion match.