tungsten foil is a common form of tungsten alloy. It is often used in electrical applications such as light bulbs, packaging materials and cables. It is also a very popular material for metallurgical machinery and shipbuilding.
Production of tungsten foil begins with powdered tungsten ore that is molded into a bar shape, then cold or hot-rolled into flat sheets and flattened into a foil. These are then heated and cooled in a vacuum annealing furnace to fortify the tungsten. Equipment for this process includes various mills, straighteners, hydraulic plate shears, water jets, and pressing machines.
The tensile properties of a tungsten foil are dominated by plastic deformation. This is evident in the engineering stress-strain curves and is associated with serrated flow as shown in EBSD analyses (Fig. 12).
Dislocations are generated in large numbers at nucleation sites. This is followed by strain localisation and propagation and dislocation-surface-interactions.
This results in a plastic zone ahead of the crack tip and a shielding dislocation free zone behind it (Fig. 14B). This is further accompanied by dislocation annihilation at the foil surface.
Despite the high brittle-to-ductile transition temperature, the plastic deformation in a severely cold-rolled tungsten plate still exhibits considerable tensile strength (Fig. 7). However, there is significant crack deflection, which we attribute to thermally activated plastic deformation. The dissipated energy for this fracture mechanism increases with increasing test temperature. This is because, for a given energy input, more tungsten sheets deform plastically at a higher test temperature than at room temperature.