Defense Intelligence Reference Document Metallic Glasses For Aerospace Applications

UNCLASSIFIED,',SFQR: 8PPlll'2L t.tl!IE e,ttY
Metallic glass foams (see above) also provide Intriguing possibilities for structural
applications. It has recently been-shown that metallic glass foams with outstanding
strength can be formed by controlling the size of the ligaments between pores. 40 This is
a new development, and these foams have not been fully characterized, but it seems
likely that optimized foams will have a specific stiffness (E/p) superior to that of
polymer foams, along with high strength and acoustic damping. Such structural foams
could be useful in applications requiring strength and stiffness under compressive loads,
such as structural panels for extraterrestrial buildings. Conceivably, such structural
foams might even be produced an site (from raw feedstock), reducing the volume of
material that needs to be launched.
A final possibility is that metallic glasses might be combined with polymer composites
into metal-fiber laminate materials. Similar laminates (with crystalline aluminum alloys)
are being employed in large quantities on the new Airbus 380 and are likely to find
increased application in the future. 41 The use of metallic glasses in these laminates is
appealing because of their high specific strength (although the specific stiffness is lower
than that of aluminum). Furthermore, the individual layers in the laminate are
sufficiently thin that a wide range of glass-forming alloys might be considered (in
contrast to thicker structural sections, which will be limited by the glass-forming ability
of the alloy).
OTHER APPLICATIONS
Monolithic metallic glasses are unique among metallic materials in having no
microstructure at length scales of more than a few atomic spacings. In principle then,
metallic glasses should be capable of replicating features down .to this scale. This
possibility is facilitated by the ability of metallic glasses to be formed in the supercooled
liquid temperature range with controllable viscosity. Indeed, superplastic forming of
metallic glass surfaces with features as small as 13 nanometers has been
demonstrated.42 This ability could be exploited for direct embossing of nanostructures
in polymers or other materials. Structures on this length scale are also potentially
useful as diffraction gratings for ultraviolet and soft x-ray radiation.
In a related area, metallic glasses have a variety of useful properties for application in
micro-electromechanical system (MEMS} actuators, including large elastic strains and
high resilience (elastic strain energy storage), good corrosion and wear resistance, and
an excellent surface finish. 43 The scale of these devices is smaller than the plastic zone
size (Equation 1 above), making brittle fracture.unlikely. Furthermore, a much wider
variety of amorphous alloys can be made In thin film form (by vapor deposition) than is
possible by casting.
Finally, the magnetic properties of certain amorphous alloys have long been exploited.
For instance, their low coercivity and high electrical resistivity make ferromagnetic
amorphous alloys attractive as high-efficiency electrical transformers, particularly at
high frequencies. Such applications are likely to continue well into the future.
19
UNCLASSIFIED/,'FOA 8FFIGll2L 1181 8Nklf