AAWSAP DIRD, Metallic Glasses for Aerospace Applications, December 2009

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Fatigue resistance (including resistance to both fatigue crack initiation and fatigue
crack growth).
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Corrosion resistance (including stress-corrosion cracking).
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Cost (including raw materials, shaping, and assembly).
Figure 9 illustrates the mechanical properties of metallic glasses and metallic glass
matrix 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 (cry /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 (Klc) against modulus (E), we can also
compare the fracture energy (Glc ~ (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 glass 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.
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