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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/ /FOA &FFI&IAb lltSE 8HL'l • Fatigue resistance (including resistance to both fatigue crack initiation and fatigue crack growth). • Corrosion resistance (including stress-corrosion cracking). • Cost (including raw materials, shaping, and assembly). Figure 9 illustrates the mechanical properties of metallic glasses and metallic glass matrix composites compared with other structural materials. Since weight is a particular concern in aerospace applications, in Figure 9(a) we normalize both yield strength (cry) and stiffness (E) to density (p); two materials with the same specific strength (cry /p) or specific stiffness (E/p) could be used to produce a component with the same overall strength or stiffness, respectively, at the same weight. Materials in the upper-right corner of the plot have the best combination of strength and stiffness for a given weight. Notice that the metallic glasses (and dendritic composites) can be stronger than virtually all crystalline metals, although the stiffness of metallic glasses tends to be somewhat smaller than that of crystalline alloys of similar composition. Figure 9(b) illustrates the damage tolerance of metallic glasses compared with other materials. By plotting the fracture toughness (Klc) against modulus (E), we can also compare the fracture energy (Glc ~ (Klc)2/E) of the materials; the dashed diagonal lines are lines of constant fracture energy . Figure 9(b) reveals several interesting aspects of the damage tolerance of metallic glasses. First, although the fracture toughness of some metallic glasses is comparable to that of crystalline metals, some metallic glasses- most notably those based on iron (Fe) and magnesium (Mg) - are as brittle as any ceramic. Second, both the fracture toughness and the fracture energy of the dendritic metallic glass matrix composites can be superior to those of all but the most fracture-resistant metals. These considerations suggest the dendritic metallic glass matrix composites might indeed find applications as structural materials in aircraft and/or spacecraft. The most obvious applications would be to replace steel in certain components where strength is critical but space is limited. These might include pylon structures and landing gear,38 although it has yet to be demonstrated that the composites can be fabricated in the sizes necessary. Furthermore, the corrosion and stress-corrosion cracking resistance of these materials has not been fully evaluated. 17 UNCLASSIFIED/ /FOR 8ffle!AL ts5E 014Lt
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