Invited Lecture
Understanding dislocation twin boundary interactions: From single twin boundaries towards nanotwinned materials

Nanotwinned materials are known for their enormous strength in combination with an outstanding ductility [1, 2]. Nevertheless, fundamental questions of their deformation behavior are still unanswered today. In the recent past it was proposed that screw dislocation transmit through coherent twin boundaries in copper by a cross-slip-like process. The process also quantitatively fits cross-slip: (i) the stress required for the constriction of two partial dislocations is identical to the transmission stress [3, 4], and (ii), the activation volume of dislocation slip transmission is similar to cross-slip [5]. However, these studies were conducted on a single coherent twin boundary on Cu.

Within this talk we will extend our findings for multiple twin boundaries in Ag. We will present physical vapour deposited Ag thin films with a twin spacing ranging from 20nm to 1µm. Besides the twin-size-scaling we will also discuss statistical aspects of dislocation slip transfer including the role of residual dislocations stored at twin boundaries as well as detwinning. Finally, we will propose a unique dislocation source mechanism at twin boundaries.

1. Lu, K., Stabilizing nanostructures in metals using grain and twin boundary architectures. Nature Reviews Materials, 2016. 1.
2. Lu, K., L. Lu, and S. Suresh, Strengthening Materials by Engineering Coherent Internal Boundaries at the Nanoscale. Science, 2009. 324(5925): p. 349-352.
3. Caillard, D. and J.L. Martin, Some aspects of cross-slip mechanisms in metals and alloys. Journal de Physique, 1989. 50(18).
4. Malyar, N.V., et al., Dislocation-twin boundary interaction in small scale Cu bi-crystals loaded in different crystallographic directions. Acta Materialia, 2017. 129: p. 91-97.
5. Malyar, N.V., et al., Dislocation slip transmission through a coherent Σ3{111} copper twin boundary: Strain rate sensitivity, activation volume and strength distribution function. Acta Materialia, 2018.