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.
“metallic”29 pages
UNCLASSIFIED/s'Pen. 8PPIIIJIIL -..sl!! fJULY deformation can proceed in a stable manner by generation and subsequent arrest of shear bands. The key to composite design is to produce a microstructure with the correct length scale to prevent propagating shear bands from becoming catastrophic cracks. This turns out to be relatively difficult with ex situ composites, for reasons of processing described above. As a result, the recently developed dendritic in situ composites have the most promising properties, and we focus the remainder of our discussion on them. STRENGTH AND DUCTILITY: PLASTIC DEFORMATION As with other composite materials, the yield strength of metallic glass matrix composites can be approximated as a simple rule of mixtures based on the volume fraction of the two phases. Because the ductile crystalline phases useful for limiting shear band propagation are weaker than the amorphous matrix, in producing a composite, some sacrifice in strength is inevitable. However, the gains in tensile ductility can be significant. For instance, monolithic titanium-based metallic glasses (like all metallic glasses) have essentially zero tensile ductility, but in situ composites based on titanium have been reported with tensile elongation as large as 12 percent. 35 This is comparable to the ductility of Ti-6Al-4V (the most common conventional titanium alloy), but in a material with about 30 percent greater strength. The properties of metallic glass matrix composites and more conventional materials are further compared below. FRACTURE AND FATIGUE The development of a stable plastic zone means additional energy is required for crack propagation, making in situ composites much more resistant to fracture and fatigue than are single-phase glasses. For instance, the plane-strain fracture toughness of some zirconium-based in situ composites can exceed 170 MPa m 112-7 times greater than that of single-phase glasses and greater than that of virtually any other metallic alloy.36 This resistance to crack propagation is also manifested as improved fatigue performance. The fatigue strength of the zirconium-based in situ composites is 20-30 percent of the tensile strength; in comparison, monolithic metallic glasses have a fatigue strength of only ~ 5 percent of the tensile strength. 37 The fatigue strength of the in situ composltes is thus comparable to that of conventional structural alloys. Aerospace Applications of Metallic Glasses STRUCTURAL APPLICATIONS The key properties of materials for structural applications in aerospace are: • Strength. • Stiffness (Young's modulus). • Density (weight). • Fracture toughness (damage tolerance). 16 UNCLASSIFil:D,'f Pl!Ut o,,1e11111: U81! 8HLY
Not linked to a story yet.
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.