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: An apparatus and a method for measuring the temperature of a reactive metallic workpiece sealed within a retort prior to and during diffusion bonding of the workpiece. The apparatus includes temperature measuring instruments disposed adjacent preselected portions of the workpiece within the retort, thermal conducting means connecting the instruments with display devices located outside the retort, conduits coupled with the interior of the retort and with the display devices, each of the conduits including a first end portion communicating the interior of the retort with vacuum generating means and a second end portion including at least one tubular region through which the thermal conducting means pass to connect with the display devices, and means for sealing the first and second end portions to maintain an evacuated state within the retort after a vacuum is applied thereto.

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.

Abstract: The invention resides in the fabrication of a structural element comprising a laminated composite having one portion or layer comprising alpha-phase titanium aluminide and another adjacent portion or layer comprising gamma-phase titanium aluminide. Preferably, the gamma-phase portion or layer is joined with the alpha-phase portion or layer by such processes as hot-spraying, diffusion bonding, or vapor deposition. The invention contemplates the utilization of the structural element in the fabrication of the wall of a container or tank for storage of the hydrogen fuel material, where the gamma-phase titanium aluminide portion or layer is oriented so as to be placed in direct contact with the hydrogen fuel material, or at the least be oriented toward any hydrogen leak path.

Abstract: A method for fabricating of intermetallic titanium aluminide sandwich structures in which blanks of titanium aluminide are bonded to one another, under vacuum in a retort, at selected areas to form a pack, and then, upon removal of the retort, expanded superplastically to form a desired sandwich structure. Bonding of the various preselected areas of the metal blanks is accomplished using elevated temperature gas diffusion bonding techniques. The invention contemplates a first thermal cycle during which the pack is diffusion bonded in an evacuated retort at one temperature within a predetermined range of temperatures, and a second thermal cycle during which subsequent superplastic forming of the pack of bonded blanks, with the retort removed, is carried out. Optionally, during the first thermal cycle, a step of superplastic preforming may be carried out whereby the pack is preformed against arcuate or other shaped forming members.

Abstract: The present invention is a method of determining oxidation on a titanium aluminide material. An aqueous saturated solution of oxalic acid is prepared. The saturated solution of oxalic acid is combined with a minor portion of hydrofluoric acid solution. The resultant oxalic acid/hydrofluoric acid solution is mixed. The titanium aluminide material is immersed in the mixed solution for a sufficiently long period to allow exposure of the oxidized surface followed by inspection thereof for a white layer indicating the presence of oxidation on its surface.

Abstract: A forming method for sealing sheet structure between two forming members wherein the sheets are subjected to high process temperatures and a high pressure differential. The method includes a heat treatment of a flaked graphite seal material to a temperature in excess of the process temperature to remove volatile contaminants therefrom.