Carbon fiber (CF) and carbon fiber composites have gained widespread use in recent years due to their unique combination of high strength and stiffness-to-weight ratio. To improve their mechanical properties, CF is sometimes used as a laminate, usually with aluminum, to improve the impact and residual strength properties of the CF. By bonding sheets of CF and aluminum, it was noticed that fatigue crack growth rates could be reduced in the laminates, as compared to monolithic sheets of either material. These composites have been referred to as CF metal laminates (CFMLs), and they are generally comprised of thin sheets of metal alloys (not always Al) and plies of fiber (not always carbon fiber) reinforced with polymeric materials.
Metallic glass used as a laminate in a fiber metal laminate (FML) allows for the development of a new class of composites that wasn't possible before. Metallic glasses are multi-component metal alloys with low melting temperatures such that when they are rapidly cooled from the liquid, they form a glass. Metallic glass ribbon, in thicknesses between 10 and 100 micrometers, has been widely fabricated since the 1960s for use in transformer coils and radio frequency identification (RFID) tags. Because metallic glasses have an amorphous (non-crystalline) atomic structure, they possess a unique combination of properties that cannot be obtained in crystalline metals.
The current innovation involves the fabrication of FMLs and specifically, CFMLs, that contain sheets of metallic glass as some or all of the metal layers. Metallic glass sheets with thicknesses between 10 and 100 µm can be fabricated by melt-spinning to form long ribbons that can then be cut and integrated into the fiber laminate either as single sheets, by weaving, by stacking, or by overlaying. Thicker sheets, from 0.1 to 1 mm thick, can be fabricated by twin-roll casting, and can be applied in the same way but where higher strength or ballistic performance is needed from the FML. The metallic glass sheets can be applied as an interior layer or as the external layer of the composite to provide a hard metallic surface to CF, for example. The number of layers can vary from one to several dozen layers of metallic glass, and the layers of the composite can be alternated with other metal layers. The integration of metallic glass into FMLs can be used for increased strength, protection of the fibers against environmental effects, increased hardness, high corrosion resistance, increased ballistic performance, high elasticity, high strength, magnetism, increased toughness, increased fatigue resistance, and low cost.
The process for fabricating metallic glass FMLs involves cutting the fibers to the correct shape for the application (such as CF pre-preg), laying-up alternating layers of fibers and metallic glass, and then curing in an autoclave or a vacuum bag. The final FML can have thickness from 1 to 20 mm, depending on the application. In some cases, the FML may need to be backed with another material, such as a polymer for radiation shielding, or some soft layer for ballistic shielding.