Documents / Report
The Defense Intelligence Agency issued this Defense Intelligence Reference Document (DIA-08-0911-012), dated 14 December 2009, as one of its FY 2009 advanced technology reports under the Advanced Aerospace Weapon System Applications (AAWSA) Program. It reviews how metallic glasses are structured and processed, their mechanical properties, and metallic glass matrix composites. It concludes that dendritic composites could replace high-strength steels in some aerospace parts. It adds that wide aerospace use depends critically on developing new lightweight glass-forming alloys.
UNCLASSIFIED,'/PBR: 8PPIIIAk W&E O•lkY - -- - --- ~.\\V•1~.•.~,\\:\~\\~,',',•,\~\\\~\\\~\\\'+~ ... 'a 3 0 .... ' r 0 -· .... ·-.. Figure 7. Cast Metalllc Glass Wedge. Wedge of a zirconium-based bulk metallic glass produced by casting. Note the sntny metallic luster, typical of metalllc glasses.21 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 ductile 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 speaking1 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 partlcles 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,'fFOlt orr1e1J11t tJ9E! OHt f
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Report, from the dia 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.