Ductility and Brittle Fracture of Tungsten by Disconnection Pile-up on Twin Boundaries

TL;DR

This study uses advanced molecular dynamics simulations to uncover how microstructural features influence ductility and brittle fracture in tungsten, providing insights into reducing the brittle-to-ductile transition temperature in BCC metals.

Contribution

It introduces a cross-scale MD simulation approach to connect atomic-scale defect dynamics with macroscopic fracture behavior in tungsten.

Findings

Dislocation starvation and twin boundary pinning lead to crack initiation.

Disconnection pile-ups at twin boundaries trigger low-stress fracture.

Microstructural control can potentially lower the DBTT in tungsten.

Abstract

Refractory body-centered cubic (BCC) metals and alloys are of extraordinary importance in modern technological and structural applications. However, their wider adoption in science and technology is severely restricted by low-temperature brittleness, quantified by an unacceptably high value of the brittle-to ductile transition temperature (DBTT). The DBTT of these alloys is known to depend strongly on the particular microstructure of the material following mechanisms that are not well understood. Here we apply cross-scale molecular dynamics (MD), a simulation approach that preserves full atomic resolution while capturing the collective evolution of dislocations, twins, and cracks in near-micron-scale volumes, to investigate ductility and fracture in single-crystal tungsten pillars as a function of initial defect microstructure, deformation conditions, and temperature. The simulations reveal a sequence of microscopic processes conducive to failure: dislocation starvation, nucleation and growth of twins, pinning of the twin boundaries at surface asperities, resulting in disconnection pile-ups that trigger crack nucleation and propagation at low macroscopic stresses along incoherent boundary segments. By resolving these processes within a single atomistic framework, our simulations connect defect-level dynamics to macroscopic fracture behavior and identify microstructural pathways capable of shifting the DBTT through targeted promotion or suppression of the underlying deformation mechanisms.