Abstract: A stack of metallic sheets is constructed for selective diffusion bonding followed by superplastic forming to yield a metallic sandwich structure. The invention resides in the provision of gas distribution channels in the stack for assuring balanced and complete distribution of gas throughout the unbonded areas of the stack. The gas is used for expansion of the stack into a sandwich structure during the step of superplastic forming. The novel construction of each channel comprises superimposed grooves in opposed face sheets of the stack and slots in the core sheet(s) of the stack.

Abstract: A retort for use in diffusion bonding preselected areas of a stack of metallic sheets during a process of fabricating metallic sandwich structures. The retort facilitates a contamination-free, evacuated environment in which a plurality of sheets of titanium aluminide can be joined to one another at selected areas to form a pack. The process of joining embraces a technique of elevated temperature gas diffusion bonding. Subsequent superplastic expansion of the bonded blanks is employed to form desired sandwich structures.

Abstract: Dummy needles are used for preventing closure of gas-conveying passageways communicating the interior, and provided at the peripery, of a multi-sheet stack of titanium alloy materials during diffusion bonding. After the diffusion bonding has been carried out, the dummy needles fitted within the passageways are removed, the passageways are reamed out to ensure their circular shape, and needles adapted for superplastic forming are inserted into the newly reamed passageways.