Deformation and failure by weaving dislocation networks in body-centered-cubic tungsten

Dislocation is the primary carrier for accommodating plastic deformation in metals. It is generally envisaged that metals with low initial dislocation density have high strain-to-failure and good formability, and vice versa. However, contrary to most metals, body-centered-cubic pure tungsten becomes brittle after reducing its dislocation density by recrystallization, while its formability increases after heavy deformation. To elucidate the mechanism of this counterintuitive mechanical behavior, by combining ex-situ indentation tests and dislocation reconstruction techniques, we find that tungsten's deformation and failure processes are accompanied by the formation of a specific dislocation pattern. Dislocation networks are governed by a mechanism similar to the weaving process of the spider's orb web. After heavy deformation, subgrains are generated due to the weaving process. The recurring weaving of dislocations reduces the mean free path for crack propagation, which is considered as the main reason for the increased formability of tungsten after deformation.