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AssigneeRockwell International Corporation
InventorsEdward D. Weisert, Suphal P. Agrawal
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A method for fabricating superplastically formed/diffusion bonded structures wherein metal blanks of a titanium alloy are joined at selected areas by diffusion bonding and expanded superplastically to form a desired sandwich or integrally stiffened structure. In such method, the metal blanks are treated in selected areas with a "stopoff" material to prevent bonding at those areas during diffusion bonding and to permit forming or shaping at the same areas during superplastic forming. An improved stopoff compound is provided for this purpose, in the form of yttria of relatively coarse particle size, coarser than 5 microns, in a suitable volatilizable vehicle. Such stopoff compound is inert to reactive metals such as titanium at the high diffusion bonding temperatures, and permits relatively low breakthrough pressure-time product during superplastic forming, thereby preventing excessive strain or rupture of the metal through non-superplastic deformation.
In the process for making a structure formed of at least two metallic workpieces of a reactive metal including the steps of treating said workpieces at selected areas with a stop-off composition to prevent bonding at said selected areas, placing said at least two workpieces into contact with each other, maintaining said workpieces under coordinated temperature-pressure-time duration conditions to produce diffusion bonding of said workpieces at preselected areas, and applying gas pressure between the contacting surfaces of said at least two workpieces to cause breakthrough at said selected areas and superplastic forming of at least one of said workpieces to stretch substantially in excess of its original surface area;
Dependencies are inferred from the claim text.