Effect of sub-surface hydrogen on intrinsic crack tip plasticity in aluminium

ABSTRACT

The effects of sub-surface hydrogen and mixed mode loading on dislocation emission in aluminium are studied using a combination of techniques including crack simulations with an empirical interatomic potential, generalised stacking fault energy (GSF) calculations, with empirical interactions and Density Functional Theory, and the model by Rice which links the critical stress intensity factor to the unstable stacking energy. The crack orientation is $\{111\}⟨112⟩$ and the loading is composed of a moderate traction along $⟨111⟩$ and a shear along $⟨112⟩$, such that Shockley partials are emitted along the crack plane. The role of the relaxations around the H atoms and of the concentration of H in the glide plane, in the GSF calculation, is revealed by comparing Rice's model to the results of brute force simulations. The enhanced GSF is then calculated ab initio. The conclusion is a large decrease of the critical load to emit a dislocation, due to the displacement transverse to the glide direction. The effect of sub-surface hydrogen is negligible with respect to the mechanical one.

KEYWORDS:

• Aluminium
• atomistic simulation
• cracking
• dislocations
• fracture
• hydrogen in metals

Acknowledgments

This work was granted access to the HPC resources of CALMIP (CICT Toulouse, France) under the allocations 2014-p0912 and 2014-p0749.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors acknowledge the support of the French Agence Nationale de la Recherche (ANR), under grant EcHyDNA (Blanc 10-19424).