AAWSAP DIRD, Metallic Glasses for Aerospace Applications, December 2009

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.

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Metallic Glasses
STRUCTURE
The atomic-scale structure of most metals and alloys is crystalline; that is, the atoms
are arranged in a highly ordered manner on a lattice that is periodic in three
dimensions, as depicted in Figure l(a). In contrast to this crystalline structure, metallic
glasses lack the long -range order of a lattice and are therefore said to be amorphous,
as depicted in Figure l(b) . Although the word "amorphous" implies a complete lack of
structural order, in fact the atomic structure of metallic glasses is not truly random.
Constraints on atomic packing provide strong short-range order; for instance, on
average the atoms have a particular number of nearest atomic neighbors at a well
defined distance. But this short-range order persists only over distances of a few
atoms; there is no long -range order as there is in a crystalline alloy. In many ways, the
atomic-scale structure of metallic glasses more closely resembles the highly disordered
structure of a liquid than the structure of a crystalline alloy.
Cry ta ll in Amorph u (gla s)
Figure 1, Amorphous Versus Crystalline Structure. Schematic atomic-scale structure of crystalline
(a) and amorphous (b) metals. In a crystalline structure, order persists over long distances (many
atomic dimensions}. In a glass, there is short range order but no long-range order.
A corollary of this difference in structure is that the nature of structural defects is quite
different between crystalline and amorphous alloys. Crystalline alloys, for example,
have extended linear defects in the crystal structure, called dislocations, that are (in
large part) responsible for determining mechanical behavior. The lack of crystalline
order precludes the existence of dislocations in metallic glasses, but other sorts of
defects can be present and may influence properties and behavior.
From an applications point of view, the amorphous structure of metallic glasses has two
principal implications. First, the mechanical properties of amorphous alloys are
significantly different from those of their crystalline counterparts; some of these
differences are advantageous, but others are not. Second, because metallic glasses are
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