Manufacturing & Prototyping

Weld Repair of a Directionally Solidified Superalloy Article

The weld is also directionally solidified to preserve the desired grain structure. An arc-welding technique for repair of a directionally solidified (DS) nickel-base superalloy article (e.g., a turbine blade or vane) has been devised. The technique equally is applicable to a part as cast or a part that has been damaged in use. Unlike ordinary gas tungsten arc (GTA) welding, this technique results in a predominantly DS microstructure in the repaired region, similar to the microstructure of the DS casting. In addition, whereas ordinary GTA welding often involves the use of a filler material different from that of the workpiece, the weld filler material used in the present technique is of the same composition as that of the DS casting, so that undesired localized chemical differences are not introduced into in the repair region.

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Low-Temperature Thermocompressive Au-to-Au Diffusion Bonding

This technique is suitable for fabrication of microelectro- mechanical structures. A technique of thermocompressive gold-to-gold diffusion bonding at relatively low temperature has been devised to provide stable, uniform, strong bonds between struc- tural components of microelectromechanical systems. The technique can also be used for vacuum sealing of microscopic cavities. Unlike some other metal-to-metal diffusion bonding techniques, this technique does not entail significant outgassing or the formation of intermetallic compounds. The technique is suitable for bonding of parts made of silicon, quartz, low-thermal-expansion glass, and other materials that can withstand the relatively mild rigors of a low-temperature thermocompressive-bonding process. Two parts to be joined by this technique must have faying surfaces that are either flat or shaped to fit each other. In preparation for bonding, each of the faying surfaces is coated with a layer of chromium, then with a layer of gold (see figure). The coating is done by electron-beam evaporation. The coated substrates are cleaned, then clamped together with their gold layers touching in the desired final configuration in a press in a vacuum chamber.

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Process for Rapid Prototyping in Ceramic-Matrix Composites

Precursors of continuous-fiber-reinforced CMCs are deposited in patterned layers. The ceramic-composite advanced tow- placement (CCATP) process is a means of laying down continuous-fiber-reinforced, ceramic-matrix composite (CMC) materials in patterned layers to form objects that could have complex three-dimensional shapes. The CCATP process is a member of the growing family of solid-freeform processes in art of rapid prototyping.

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Growing Carbon Nanotubes Aligned With Patterns

Positions and orientations of individual nanotubes could be tailored. A process has been proposed for growing carbon nanotubes aligned substantially parallel with the nominal planar surfaces of substrates and further aligned with patterns on the substrates. Prior to growth, the patterns would be formed by micromachining the substrates, which could be silicon or siliconon- insulator (SOI) wafers. By making it possible to tailor the positions and orientations of individual carbon nanotubes grown on pre-patterned substrates, this process would enable advances in nanotube-based electronic and electromechanical devices.

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Use of Nanofibers to Strengthen Hydrogels of Silica, Other Oxides, and Aerogels

Research has shown that including up to 5 percent w/w carbon nanofibers in a silica backbone of polymer crosslinked aerogels improves its strength, tripling compressive modulus and increasing tensile stress-at-break fivefold with no increase in density or decrease in porosity. In addition, the initial silica hydrogels, which are produced as a first step in manufacturing the aerogels, can be quite fragile and difficult to handle before cross-linking. The addition of the carbon nanofiber also improves the strength of the initial hydrogels before cross-linking, improving the manufacturing process. This can also be extended to other oxide aerogels, such as alumina or aluminosilicates, and other nanofiber types, such as silicon carbide.

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Two Concepts for Deployable Trusses

Thermal-actuation and misalignment-tolerant double-pivot designs are proposed.Two concepts that could be applied separately or together have been suggested to enhance the utility of deployable truss structures. The concepts were intended originally for application to a truss structure to be folded for compact stowage during transport and subsequently deployed in outer space. The concepts may also be applicable, with some limitations, to deployable truss structures designed to be used on Earth.

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External Adhesive Pressure-Wall Patch

A hole in a pressure wall can be patched, without need for previously installed faste A mechanical device has been developed for applying an adhesive patch, from the outside, to the wall of a spacecraft module that has lost pressure because of penetration by a meteoroid or a piece of orbital debris. This device will make it possible to seal and re-pressurize the affected module during space flight. Devices identical or similar to this one might also prove useful in the repair of other pressurized bodies and similar objects, including gas and oil pipes and ship hulls, for example.

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