Abstract
Although hydrogen embrittlement has been observed and extensively studied in a wide variety of metals and alloys, there still exist controversies over the underlying mechanisms and a fundamental understanding of hydrogen embrittlement in nanostructures is almost non-existent. Here we use metallic nanowires (NWs) as a platform to study hydrogen embrittlement in nanostructures where deformation and failure are dominated by dislocation nucleation. Based on quantitative in-situ transmission electron microscopy nanomechanical testing and molecular dynamics simulations, we report enhanced yield strength and a transition in failure mechanism from distributed plasticity to localized necking in penta-twinned Ag NWs due to the presence of surface-adsorbed hydrogen. In-situ stress relaxation experiments and simulations reveal that the observed embrittlement in metallic nanowires is governed by the hydrogen-induced suppression of dislocation nucleation at the free surface of NWs.
Highlights
Hydrogen embrittlement has been observed and extensively studied in a wide variety of metals and alloys, there still exist controversies over the underlying mechanisms and a fundamental understanding of hydrogen embrittlement in nanostructures is almost non-existent
The non-uniformity effect of hydrogen could contribute to the localization of plasticity from the point of view of reduced local nucleation barrier as a hydrogen-locked site breaks free
In an elegant explanation of distributed plasticity in penta-twinned NWs24, a dislocation nucleation event increases the local activation energy and immediately causes its nucleation site to be locked up, and further nucleation is shifted to a neighboring site where activation energy has not been raised
Summary
Hydrogen embrittlement has been observed and extensively studied in a wide variety of metals and alloys, there still exist controversies over the underlying mechanisms and a fundamental understanding of hydrogen embrittlement in nanostructures is almost non-existent. A chemomechanical origin of hydrogen trapping and segregation at grain boundaries was revealed in recent atomic level studies of HE21,22 Most of these existing studies focused on the movement, multiplication, and interaction of dislocations with solute hydrogen in a bulk material and very little is known about whether HE exists in nanostructures where dislocation nucleation plays a dominant role in deformation mechanisms[23,24,25,26]. In-situ stress relaxation experiments and simulations reveal that the underlying mechanism of HE in NWs is the hydrogen-induced suppression of surface nucleation of dislocations, leading to higher yield strength and failure by localized necking in pentatwinned Ag NWs in a hydrogen environment
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