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This Defense Intelligence Reference Document, dated 14 December 2009, was prepared by the Defense Intelligence Agency's Defense Warning Office under its Advanced Aerospace Weapon System Applications program. It is a technical review of metallic glasses that covers their structure, processing, mechanical behavior and possible aerospace uses. It concludes that composites with ductile dendrites in a glass matrix hold the most promise for structural use. It also finds that widespread aerospace adoption depends on developing new lightweight glass-forming alloys.
From the source: Release of 2026-09-18 Incident: 12/14/09, Las Vegas, Nevada. Released with redactions. This document is a Defense Intelligence Reference Document (DIRD), a technical reference format used by the Defense Intelligence Agency (DIA) to capture baseline knowledge on a specific topic for later analytic use. DIRDs are best understood as reference and synthesis products rather than as original research. It is one of 38 DIRDs produced under the Advanced Aerospace Weapon System Applications Program (AAWSAP) between 2009 and 2011. Because AAWSAP’s scope permitted a broad range of supporting topics, not every DIRD in the series directly concerns aerospace systems or future threat assessment. The following summary reflects the DIRD’s scope and framing at the time of writing and should not be read as implying current validation of the concepts discussed. This DIRD surveys metallic glasses as a potentially important class of aerospace materials and describes their amorphous structure as offering very high strength and unusual manufacturing advantages, but also significant drawbacks, especially poor ductility and fatigue resistance. The document concludes that the most promising aerospace applications are likely to come from metallic-glass-matrix composites rather than single-phase glasses, because these composites can retain high strength while greatly improving fracture toughness and fatigue performance, potentially enough to substitute for high-strength steels in some space-limited structural uses. At the same time, the report judges that broader aerospace use will depend on substantial progress over the next 20–50 years in alloy design, processing, and especially the development of lightweight systems, including aluminum-based options.
UNCLASSIFIED//POI\ OPP!elAL ~SI: 8,.LY and thus reduce the window of time available for molding. In practice, therefore, successful molding requires careful control of the processing conditions. Joining Structural applications inevitably require joining of components, for instance by mechanical fasteners or adhesives or by welding, soldering, or brazing. The use of fasteners and adhesives is much the same for metallic glasses as for any other metal. Techniques such as welding, soldering, and brazing are potentially problematic because they involve heating the glassy alloy, running the risk of crystallization (which could make the joint more brittle) . In welding, for instance, the metal to be joined is actually melted and then resolid ifies upon cooling. In the case of a metallic glass, care must be taken to ensure the cooling rate is fast enough to avoid crystallization. There is also a risk that the glassy material in the heat-affected zone (near to but not in the molten region) might crystallize. Laboratory tests of a variety of welding techniques have been performed on several glass-forming alloys with mixed results, and it is clear that much remains to be done in this area. Foams One particularly promising recent development is the ability to produce metallic glass foams. Here, the relatively high viscosity of glass-forming alloys is an advantage in producing a stable foam structure that can be solidified, leaving a high-porosity foam with metallic glass ligaments. 9 These foams have high specific strength (that is, strength normalized to density) and specific stiffness and could have excellent damage tolerance, although this has not been demonstrated. Thin Films and Coatings The discussion above focuses on the processing of free-standing metallic glasses, with an emphasis on structural applications. However, it is also possible to produce amorphous alloys as thin films or coatings using techniques such as physical vapor deposition or electrodeposition. Although the thicknesses of material that can be produced in this way are limited, they are useful for making amorphous alloy coatings (for wear and corrosion resistance) or for thin films for magnetic or micro electromechanical system (MEMS) applications. A distinct advantage of the thin film techniques is that because the effective cooling rates during vapor deposition are extremely high, a much wider range of alloys can be produced in amorphous form than is possible with casting. This allows the alloy composition to be tailored for optimization of functional properties, with less concern about glass-forming ability. Mechanical Behavior Near Room Temperature When a material is subjected to a stress, it can experience both elastic and plastic deformations. Elastic deformation occurs at lower stresses and is recoverable when the applied stress is removed. The limit of elastic deformation is defined by the yield stress- the point at which plastic (nonrecoverable) deformation begins. Much of the current interest in metallic glasses arises because their yield stresses (that is, their strengths) can be much higher than those of crystalline alloys of similar composition; this difference is a direct result of the novel atomic-scale structure of metallic glasses. The fracture and fatigue characteristics of metallic glasses are also different from those 5 UNCLASSIFIED/ /FOA OFFI&ilAb WS& 8PtLY
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Official release, from the pursue collection. The PDF is mirrored here; the original link is above. 30 pages are in the text index: search them above, or from the library's search.