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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.
“The Advance”7 pages
UNCLASSIFIEL/j1P91l err1e:1•t tl!H! eHtY 200 Jtm figure 4. Shear Bands. Produced by bending of a zirconium-based metallic glass. 14 Fracture Toughness Fracture toughness is a measure of a material's resistance to growth of cracks, a critical property for structural materials subjected to tensile loading. In very tough metals, the toughness usually results from plastic deformation that occurs near the tip of the advancing crack; plastic deformation requires energy, and the need to provide this energy translates into resistance to crack growth. 3 Despite their lack of tensile ductility, at least some metallic glasses are not brittle in the same sense that ceramics are, for example, because they can experience significant plastic deformation around the crack tip during fracture. For instance, the fracture toughness (K1c) of zirconium-based metallic glasses is about 20 MPa,m 1l 2 15-somewhat lower than the N 55 MPa-m112 typical of crystalline zirconium alloys16 but much greater than the fracture toughness of ceramics (typically 1-5 MPa-m 1l 2). The fact that metallic glasses are reasonably tough despite their lack of tensile ductility suggests structural applications are not out of the question. However, some metallic glasses appear to be intrinsically brittle in that they fracture with only limited plastic deformation near the crack top and thus have very low values of fracture toughness. For this reason, some alloys that would otherwise be highly desirable, such as iron-based metallic glasses (for their high strength and low cost) and magnesium-based glasses (for their low density), fall into this category. The physical origins of the difference between intrinsically brittle metallic glasses and those capable of limited plastic deformation (and thus some toughness} are not well understood. 3 In other materials, notably polymer-matrix composites, other mechanisms of toughening can be more Important. B UNCLASSIFIED/;SPiUI 8PFl&liilll:: -,ge 9HLt
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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.