A dislocation dynamics study of the strength of stacking fault tetrahedra. Part I: interactions with screw dislocations

Abstract

We present a comprehensive dislocation dynamics (DD) study of the strength of stacking fault tetrahedra (SFT) to screw dislocation glide in fcc Cu. Our methodology explicitly accounts for partial dislocation reactions in fcc crystals, which allows us to provide more detailed insights into the dislocation–SFT processes than previous DD studies. The resistance due to stacking fault surfaces to dislocation cutting has been computed using atomistic simulations and added in the form of a point stress to our DD methodology. We obtain a value of 1658.9 MPa, which translates into an extra force resolved on the glide plane that dislocations must overcome before they can penetrate SFTs. In fact, we see they do not, leading to two well differentiated regimes: (i) partial dislocation reactions, resulting in partial SFT damage, and (ii) impenetrable SFT resulting in the creation of Orowan loops. We obtain SFT strength maps as a function of dislocation glide plane-SFT intersection height, interaction orientation, and dislocation line length. In general SFTs are weaker obstacles the smaller the encountered triangular area is, which has allowed us to derive simple scaling laws with the slipped area as the only variable. These laws suffice to explain all strength curves and are used to derive a simple model of dislocation–SFT strength. The stresses required to break through obstacles in the 2.5–4.8-nm size range have been computed to be 100–300 MPa, in good agreement with some experimental estimations and molecular dynamics calculations.

Keywords:

• dislocation dynamics
• stacking-fault tetrahedra
• irradiation damage
• Cu plasticity

Acknowledgements

This work was performed under the auspices of the US Department of Energy by the University of California Lawrence Livermore National Laboratory under contract No. W-7405-ENG-48 and the Laboratory-directed Research and Development Office under program 06-ERD-005. EM and JMP acknowledge support from Project P030531762/VENUS-REVE with CSN, UNESA and CIEMAT, and Spanish National Project MEC ENE2005-08266-C04-04/FTN. Fruitful discussions with H. J. Lee and B.D. Wirth are gratefully acknowledged.

Notes

Notes

1. Due to the curvature, the line sense is actually reversed, resulting in a BA segment, rather than the original AB.

2. Shearing is characterized by f _i > f*, i = 1, …, N _s where N _s is the number of nodes in contact with a stacking fault surface.