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.

UNCLASSIFIED//POI\ OPPl@IAL WS& 0,u.v
Figure 7. Cast Metallic Glass Wedge. Wedge of a zirconium -based bul k metallic glass produced by
casti ng. Note the shiny metallic luster, t ypical of metallic glasses .27
Metallic Glass Matrix Composites
As discussed above, the lack of crystalline defects gives metallic glasses high strength
but compromises their ductility and fracture toughness. In particular, the tendency for
plastic deformation to localize into shear bands prevents the material from deforming in
a "graceful" manner. So it should not be surprising that there have been many
attempts to control shear band initiation and propagation by making composite
materials consisting of particles or fibers of some other material (most commonly a
ducti le crystalline metal) in a metallic glass matrix. The idea is to produce a material
with improved ductility, fracture toughness, and fatigue properties while (hopefully) not
sacrificing the qualities- especially strength and processing flexibility - that make
metallic glasses interesting in the first place.
PROCESSING AND STRUCTURE OF COMPOSITES
Broadly speaking, there are two kinds of metallic glass matrix composites: ex situ and
in situ. In ex situ composites, the metallic glass and the crystalline phase (be it in the
form of particles or fibers) are physically combined, for instance by adding particles to
the melt before casting . In situ composites are different in that the crystalline phase is
produced directly from the melt (by precipitation) during processing . This fundamental
difference in processing leads to significant differences in structure and therefore in
properties.
13
UNCLASSIFIED/ /POI\ OPPlelAL liS! 8HLV