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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/ /EiOR QFFIEJIAL l1!E ONLY deformation can proceed in a stable manner by generation and subsequent arrest of shear bands. The key to composite design is to produce a microstructure with t he correct length scale to prevent propagating shear bands from becoming catastrophic cracks. This turns out to be relatively difficult with ex situ composites, for reasons of processing described above. As a result, the recently developed dendritlc in situ composites have the most prom ising properties, and we focus the remainder of our discussion on them. STRENGTH AND DUCTILITY: PLASTIC DEFORMATION As with other composite materials, the yield strength of metallic glass matrix composites can be approximated as a simple rule of mixtures based on the volume fraction of the two phases. Because the ductile crystalline phases useful for limiting shear band propagation are weaker than the amorphous matrix, in producing a composite, some sacrifice in strength is inevitable. However, the gains in tensi'le ductility can be significant. For instance, monolithic titanium -based metallic glasses (like all metallic glasses) have essentially zero tensile ductility, but in situ composites based on titanium have been reported with tensile elongation as large as 12 percent. 35 This is comparable to the ductility of Ti-6Al-4V (the most common conventional titanium alloy), but in a material with about 30 percent greater strength. The properties of metallic glass matrix composites and more conventional materials are further compared below. FRACTURE AND FATIGUE The development of a stable plastic zone means additional energy is required for crack propagation, making in situ composites much more resistant to fracture and fatigue than are single-phase glasses . For instance, the plane-strain fracture toughness of some zirconium -based in situ composites can exceed 170 MPa m 112 - 7 times greater than that of single-phase glasses and greater than that of virtually any other metallic alloy. 36 This resistance to crack propagation is also manifested as improved fatigue performance. The fatigue strength of the zirconium-based in situ composites is 20-30 percent of the tensile strength; in comparison, monolithic metallic glasses have a fatigue strength of only~ 5 percent of the tensile strength. 37 The fatigue strength of the in situ composites is thus comparable to that of conventional structural alloys. Aerospace Applications of Metallic Glasses STRUCTURAL APPLICATIONS The key properties of materials for structural applications in aerospace are: • Strength. • Stiffness (Young's modulus) . • Density (weight) . • Fracture toughness (damage tolerance) . 16 UNCLASSIFIED/ /FOR OFFICIO! 11S5 AN! X
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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.