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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\ OFPl@IAL WS& &Nia¥ glasses in t he true sense of the word, rather than meltin g abruptly (as crysta ll ine metals do), they soften and flow over a range of temperatures in a manner akin to common (oxide) glasses. This creates opportunities for tremendous flexibi lity in the processing of metallic glasses. PROCESSING Glass-Forming Alloys The key to making a meta ll ic glass is to retain the disordered, liq uid-like atomic sca le structure during cooling from the melt . All materials have a tendency to crystal lize upon coo lin g because the crystalline state is the most stable structure at any temper ature below the melting point. But crystallization takes time, so if the cooling is fast enough, it is possib le to bypass crysta ll ization and form an amorphous structure at the glass transition temperature (Figure 2(a)) . Glass formation and crysta llization are therefore competitive processes; wh ich one will occur depends on the material and the processing conditions. (a) (b) Temperature 101(1 Liquid ~ g_"' 10~ Me ll ii1g ,.,1ompcrarurc i§ 10 l mm) ' 0 -- - '_I I O o' ' \ ~ ' 'x,o~\ \ Pd., u.,N11,P,, . . 0 I Zr,.,T1 1,.Cu,,,N1" Bc,.,, ...._ _,, 0 Ti me 01 OJ OA 05 Oh 0~ OB Reduced glass tran ition temperature (T ,IT,,.) Figure 2. Critica l Cooling Rate. (a) Effect of the coo ling rate on glass formation - If the cooling rate l s slow (path 1), th en the melt crysta llizes befo re going through the glass transition . I f the cooling rate is fast enough (path 2), then the me lt can form a glass. The critica l cooling rate (path 3) is the slowest rate at which the melt can be cooled and still form a glass. (b) Criti ca l cooling rates for various metall ic al loys - Th e horizonta l axis is the glass tra nsition temperature nor malized to the melting (liquidus) temperature. 1 For some materials, such as silica (s il icon dioxide) and most thermoplastic polymers, the crystallization process is slow because the crystal structures are complex and the basic structura l units (for example, segments of polymer chains) are slow to rearrange into a crystalline form. These materials can therefore be prod uced in glassy form even at very low cooling rates; in fact, it can be difficult to crystallize them at all. Metals and alloys are another matter because the crystal structures are relatively simple and the basic structura l units are individual atoms, which are highly mobi le. Metal lic crystals nucleate and grow quickly, making production of a meta lli c glass more challenging. 2 UNCLASSIFI ED/ /FOA OFFICI.li.la Wili 8PU11¥
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