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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.
“metallic”29 pages
UNCLASSIFIEDl,'P811 8FPl81tf.tls Y&& &ftlsl.f of conventional alloys. In this section, we review the mechanical behavior of metallic glasses, with particular attention to properties of interest for aerospace applications. We consider actual properties in detail in the section below on applications, where we compare the properties of metallic glasses with those of other advanced structural materials. Stiffness: Elastic Deformation Stiffness is the resistance of a material to elastic deformation and is quantified by either the elastic modulus (for tensile or compressive loads) or the shear modulus (for shear loading). Metallic glasses tend to be somewhat (20-30 percent) less stiff than crystalline alloys of similar composition. The lower modulus is a consequence of the amorphous structure, in which atoms are (on average) slightly farther apart than in a crystalline alloy, enabling certain atomic relaxations that are not possible in a crystal. The lower modulus of amorphous alloys is clearly a concern in applications where stiffness is a primary criterion, but it does present some advantages. For instance, some applications (springs, for example) require the ability to store elastic strain energy (resilience), and here metallic glasses do quite well. Resilience is also a key figure of merit for snap-fit assembly of materials without fasteners. Overall, however, for structural applications, the low stiffness of metallic glasses is a disadvantage. Strength and Ductility: Plastic Deformation The theoretical strength of perfect, defect-free crystalline metals is several orders of magnitude larger than strengths measured in typical laboratory experiments. The difference exists because metallic crystals inevitably have crystalline defects (dislocations) that are able to move at relatively low stresses and cause plastic (nonrecoverable) deformation. Because dislocations cannot exist in an amorphous structure, in principle the strength of amorphous alloys should approach theoretical limits based on the inherent strength of the atomic bonds. As shown in Table 2, the strength of aluminum-based metallic glasses can be two or three times greater than those of conventional (crystalline) high-strength aluminum alloys. Similarly high strengths are seen for other amorphous alloys; for instance, the best iron-based alloys have a strength of approximately 4 GPa-again, two or three times greater than those of conventional high-strength steels. 10 Such high strengths create great interest in potential structural applicat1ons of metallic glasses. 6 UNCLASSIFIED/i'F81i1 QFFICIOh. : ■ ss ctr· X
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Report, from the dia collection. The PDF is mirrored here; the original link is under it. 30 pages are in the text index: search them above, or from the library's search.