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,'/F&R: IFFillt\L ltlll OHleY • Fatigue resistance (including resistance to both fatigue crack initiation and fatigue crack grow th). • Corrosion resistance (including stress-corrosion cracking}. • Cost (including raw materials, shaping, and assembly). Figure 9 illustrates the mechanical properties of metallic glasses and metallic glass matrh< composites compared with other structural materials. Since weight is a particular concern in aerospace applications, in Figure 9(a) we normalize both yield strength (cry) and stiffness (E) to density (p); two materials with the same specific strength (oy /p) or specific stiffness (E/p) could be used to produce a component with the same overall strength or stiffness, respectively; at the same weight. Materials in the upper-right corner of the plot have the best combination of strength and stiffness for a given weight. Notice that the metallic glasses (and dendritic composites) can be stronger than virtually all crystalline metals, although the stiffness of metallic glasses tends to be somewhat smaller than that of crystalline alloys of similar composition. Figure 9(b) illustrates the damage tolerance of metallic glasses compared with other materials. By plotting the fracture toughness (Kic) against modulus (E), we can also compare the fracture energy (Gic ::::i. (Klc)2/E) of the materials; the dashed diagonal lines are lines of constant fracture energy. Figure 9(b) reveals several interesting aspects of the damage tolerance of metallic glasses. First, although the fracture toughness of some metallic glasses is comparable to that of crystalline metals, some metallic glasses-most notably those based on iron (Fe) and magnesium (Mg)-are as brittle as any ceramic. Second, both the fracture toughness and the fracture energy of the dendritic metallic gl_ass matrix composites can be superior to those of all but the most fracture-resistant 'metals. These considerations suggest the dendritic metallic glass matrix composites might indeed find applications as structural materials in aircraft and/or spacecraft. The most obvious applications would be to replace steel in certain components where strength is critical but space is limited. These might include pylon structures and landing gear,38 although it has yet to be demonstrated that the composites can be fabricated in the sizes necessary. Furthermore, the corrosion and stress-corrosion cracking resistance of these materials has not been fully evaluated. 17 UNCLASSIFIEDJ/FOR: OFFIGltf1L \Hi'i o,11a.v
Not linked to a story yet.
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.