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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/ /FOR O&&iliCilial.ls: W&E 8,.L'l Table 2. Comparison of Strengths of Amorphous and Crystalline Aluminum Alloys. Compared with the theoretical maximum strength (taken to be μ/30, where μ is the shear modulus of pure aluminum). % of Theoretical Yield Stress (MPa) Stren th Theoretical Strength (Defect 1,600 Free Crystal) Typical High Strength Aluminum Alloy 400- 500 25- 31% (7xxx Series) 11 Best Crystalline Aluminum Alloy 12 770 48% Aluminum-Based Metallic Glass 13 1,280 80% Unfortunately, the lack of dislocations in amorphous alloys is also their Achilles' heel. In crystalline alloys, dislocations move and multiply in response to applied stresses, resulting in dislocation tangles that increase the resistance to further dislocation motion . Th is process, called strain harden ing, is of crucial importance because It makes plastic deformation stable. If one region of a crystalline material yields and begins to plastically deform, the deforming region strain hardens, and so another region will deform instead. The result is that the plastic deformation is not concentrated but rather spreads through a large volume of material. Metallic glasses, lacking dislocations, do not strain harden and in fact strain sohen in response to plastic deformation . Th is means t hat as soon as any one region yields, any further deformation will occur in the same region. This process, known as shear localizati1on, leads to the formation of shear bands (Figure 4 ). In any loading geometry where the metallic glass experiences significant tensile loading, fracture occurs on a single dominant shear band with essentially zero tensile ductility.2 Metallic glasses therefore fracture in an abrupt, apparently brittle manner on the macroscopic scale (even though there can be significant plasticit y on a microscopic scale). This lack of ductility is of obvious concern to designers interested in structural applications. Furthermore, it limits the ability to fabricate metallic glasses into different shapes by deformation processing (by rolling or forging, for instance) aher casting. 2 Th is assumes there is no geometrical constrai nt preventing fractur,e. Some geometries (such as si mple bending) can involve tensile load ing, but there can still be significant plastic deformation because the geometrica l constraints Inhibit propagating of shear bands across th e specimen. 7 UNCLASSIFIED/ /FOR OFFIGlal.ls: Wii QfilLV
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