“metallic”29 pages
- p. 1 …Defense
Intelligence
Reference
Document
Acquisition Threat Support
Metallic Glasses: Status and
Prospects for Aerospace
Applications
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Metallic Glasses: Status and Prospects for Aerospace
Applications
Prepared…
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Metallic Glass Matrix Composites ......................................................................... 13
Processing and Structure of Composites ..... ~ .................................................... 13
Ex Situ Composites ............................................................................................ 14…
- p. 4 …Examples of Processing of Metallic Glasses ........................................................ 4
4. Shear Bands ....................................................................................................... 8
5. Fatigue Limit of Metallic…
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Metallic Glasses: Status and Prospects for…
- p. 6 …in all these areas, and that metallic glasses and metallic
glass matrix composites will see increasing…
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Metallic Glasses
STRUCTURE
The atomic-scale structure of most…
- p. 8 …Metallic crystals
nucleate and grow quickly, making production of a metallic glass more challenging.
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One way to quantify the ability of a metallic alloy…
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Casting and Molding
Like other alloys, metallic glasses can be cast into…
- p. 11 …The use of
fasteners and adhesives is much the same for metallic glasses as for any…
- p. 12 …In this section, we review the mechanical behavior of metallic
glasses, with particular attention to properties…
- p. 13 …In any loading geometry where the metallic glass experiences
significant tensile loading, fracture occurs on a…
- p. 14 …Produced by bending of a zirconium-based metallic glass. 14
Fracture Toughness
Fracture toughness is a…
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Even some metallic glasses with reasonable toughness may be embrittled by…
- p. 16 …Fatigue Limit of Metallic Glasses and Metallic-Glass-Matrix Composites. Fatigue life data for
single-phase…
- p. 17 …Deformation Map for Metallic Glasses. As a function of temperature (normalized to the glass
transltlon temperature…
- p. 18 …Magnetic, Electrical, Optical, Thermal, and Acoustic
Although most of the current interest in metallic glasses centers…
- p. 19 …Wedge of a zirconium-based bulk metallic glass produced by
casting. Note the sntny metallic luster…
- p. 20 …One of the most promising recent advances in the metallic glass field is the
development of…
- p. 21 …The size of the plastic zone varies from ~ 1 μm for "intrinsically brittle"
metallic glasses to…
- p. 22 …For instance, monolithic titanium-based metallic glasses
(like all metallic glasses) have essentially zero tensile ductility…
- p. 23 …Figure 9 illustrates the mechanical properties of metallic glasses and metallic glass
matrh< composites compared with…
- p. 24 …bath normalized to density) of metallic glasses
(yellow) and dendrltic metallic glass matrix composites (red) compared…
- p. 25 …A final possibility is that metallic glasses might be combined with polymer composites
into metal-fiber…
- p. 26 …Attempts to make aluminum-based metallic glass components by
consolidating amorphous powders have met with limited…
- p. 27 …This ease of processing could
offset the higher raw materials costs for metallic glasses, making them…
- p. 28 …Summary and Recommendations
Metallic glasses combine some of the advantageous mechanical properties of metals-
strength, stiffness…
- p. 29 …Liu, Chapter 4 in Bulk Metallic Glasses, .M. Miller and P. K. Liaw, eds. (Springer, 2009…
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Casting and Molding
Like other alloys, metallic glasses can be cast into net-shape or near-net-shape
geometries. Die casting into a permanent (metal) mold-because it provides the rapid
heat transfer needed to meet the requirement for relatively rapid cooling-is the most
common casting technique. In most cases, casting is done in either a vacuum or an
inert atmosphere to prevent formation of oxide particles that promote crystallization.
Conventional casting, however, does not take advantage of the flexibility afforded by
the glassy nature of these alloys. If a metallic glass is heated to a temperature above
its glass transition temperature, it becomes a supercooled liquid. In this state, the
viscosity drops with increasing temperature over a wide range, making it possible to
control the viscosity by controlling the temperature. 1 This ability to control the viscosity
enables many of the processing techniques commonly used in molding thermoplastic
polymers to be applied to metallic glasses (Figure 3).
200 μ111
Figure 3. Examples of Processing of Metallic Glasses. (a) Microspring produced by lithography and (b) thin-
walled bottle produced by blow molding. Images are courtesy of Professor Jan Schroers (Yale University).
There are two important limitations on processing of metallic glasses in the supercooled
liquid region. First, supercooled liquids are metastable and have a tendency to
crystallize, so there is a limited window of time (typically on the order of minutes) in
which the processing must be completed if the glassy structure is to be maintained.
Second, the viscosity of many glass-forming alloys near the glass transition
temperature is too high for convenient processing. The viscosity can be reduced by
increasing the processing temperature, but higher temperatures promote crystallization
1 A crystalline metal, in contrast, melts abruptly, going from a rigid solid to a low-viscosfty fluid very quickly.
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