Solute drag on perfect and extended dislocations

Abstract

The drag force exerted on a moving dislocation by a field of mobile solutes is studied in the steady state. The drag force is numerically calculated as a function of the dislocation velocity for both perfect and extended dislocations. The sensitivity of the non-dimensionalized force–velocity curve to the various controlling parameters is assessed, and an approximate analytical force–velocity expression is given. A non-dimensional parameter S characterizing the strength of the solute-dislocation interaction, the background solute fraction , and the dislocation character angle , are found to have the strongest influence on the force–velocity curve. Within the model considered here, a perfect screw dislocation experiences no solute drag, but an extended screw dislocation experiences a non-zero drag force that is about 10 to 30% of the drag on an extended edge dislocation. The solutes can change the spacing between the Shockley partials in both stationary and moving extended dislocations, even when the stacking fault energy remains unaltered. Under certain conditions, the solutes destabilize an extended dislocation by either collapsing it into a perfect dislocation or causing the partials to separate unboundedly. It is proposed that the latter instability may lead to the formation of large faulted areas and deformation twins in low stacking fault energy materials containing solutes, consistent with experimental observations of copper and stainless steel containing hydrogen.

Keywords:

• Dislocation
• solute
• drag
• Cottrell atmosphere
• extended dislocation

Acknowledgements

The authors thank C. W. San Marchi, D. M. Barnett, and W. D. Nix for helpful comments and insight.

Notes

No potential conflict of interest was reported by the authors.

1 In a substitutional solid solution, the diffusion coefficients of the solvent and solute species are generally different, and this leads to a diffusion flux that is different from that presented here [17]. For the sake of simplicity we neglect this effect and assume the diffusivities of all atomic species are equal, yielding Equation (7(7) ).

2 It has been shown that when partial dislocations are so close that their core structures overlap, it is possible to have partial Burgers vectors that are smaller than [19]. Here we neglect this effect, and point out that in such a case the dislocation is likely well approximated as perfect for the purposes of solute drag calculation.

Additional information

Funding

This work was supported by Sandia National Laboratories (R.B.S.) and by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering [award number DE-SC0010412 (W.C.)]. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract [DE-AC04-94AL85000].