Dislocation evolution during additive manufacturing of tungsten

Additive manufacturing (AM) frequently encounters part quality issues such as geometrical inaccuracy, cracking, warping, etc. This is associated with its unique thermal and mechanical cycling during AM, as well as the material properties. Although many efforts have been spent on this problem, the underlying dislocation evolution mechanism during AM is still largely unknown, despite its essential role in the deformation and cracking behavior during AM and the properties of as-fabricated parts. In this work, a coupling method of three-dimensional dislocation dynamics and finite element method is established to disclose the mechanisms and features of dislocations during AM. Tungsten (W) is chosen as the investigated material due to its wide application. The internal thermal activated nature of dislocation mobility in W is taken into account. The correlations between the combined thermal and mechanical cycles and dislocation evolutions are disclosed. The effect of adding alloying element Ta in W is discussed from the perspectives of tuning dislocation mobility and introducing nanoparticles, which helps to understand why higher dislocation density and fewer microcracks are observed when adding Ta. The current work sheds new light on the long-standing debating of dislocation origin and evolutions in the AM field.