Effect of twin boundaries on the strength of body-centered cubic tungsten nanowires

TL;DR

This study reveals that twin boundaries in body-centered cubic tungsten nanowires can weaken their strength by promoting crack nucleation, contrasting with their typical strengthening role in other metals.

Contribution

The paper demonstrates that twin boundaries reduce the strength of BCC tungsten nanowires, challenging the conventional view of TBs as strengthening features in metals.

Findings

Twinned W nanowires have 16% lower fracture strength than single-crystal nanowires.

Cracks nucleate early at the intersection of TBs and surfaces, leading to failure.

Dislocation/TB interactions do not strengthen W due to high Peierls barrier and stacking fault energy.

Abstract

Twin boundaries (TBs) are assumed to be obstacles to dislocation motion and increase the strength of metals. Here, we report the abnormal phenomenon that TBs reduce the strength of body-centered cubic (BCC) tungsten (W). [1-11]-oriented W nanowires with (121) twin planes and free of dislocations were fabricated by chemical vapor deposition. In situ tensile tests within the transmission electron microscope were performed on single-crystal and twinned W nanowires. The fracture strength of the twinned W nanowire was 13.7 GPa, 16% lower than that of the single-crystal W nanowire (16.3 GPa). The weakening mechanism of the TB was revealed by a combination of atomic-resolution characterizations and atomistic simulations. Twinned W nanowires failed by the early nucleation of a crack at the intersection of the TB with the surface. The standard strengthening mechanism by dislocation/TB interaction was not operative in W because the high Peierls barrier and stacking fault energy in W hinder dislocation nucleation and glide. These findings provide a new insight into the influence of TBs on the mechanical properties of BCC metals.