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.
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The subject of stress-corrosion cracking of metallic glasses, despite its obvious
importance for structural applications, has received scant attention in the literature.
What little work that has been done has focused on zirconium-based glasses, with the
observation that these alloys are very susceptible to stress-corrosion cracking in
aqueous environments containing chloride ions, likely owing to the fact that they do not
form protective oxide surface layers. 22
Mechanical Behavior at Elevated Temperature
The discussion above relates to mechanical behavior at temperatures well below the
glass transition temperature. At elevated temperatures, the strength drops and plastic
deformation transitions to a homogeneous mode, occurring throughout the specimen
instead of being localized into shear bands (Figure 6). Above the glass transition
temperature, the alloy becomes a fluid, with a viscosity that drops exponentially with
increasing temperature. Because the strength of the material is low, temperatures
either above or below the glass transition may be useful for processing, as discussed
above. However, the decrease in strength and the tendency for crystallization at
elevated temperatures preclude use of metallic glasses from structural applications at
temperatures approaching the glass transition temperature.
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Figure 6. Deformation Map for Metallic Glasses. As a function of temperature (normalized to the glass
transltlon temperature) and applled shear stress i: (normalized to the shear modulus, μ). At high stresses, plastic
deformation occurs lnhomogeneously, being localized into shear bands. At high temperatures, plastic deformation
becomes homogeneous. The dashed lines represent different strain rates. The absolute stresses given are
representative of the well-studied bulk metallic glass Zr4L2Tl13.8Cu12.SNl10Be22.5, but the general features of
the map are expected to apply to all metallic glasses.73
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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.