Dislocation dynamics prediction of the strength of Al-Cu alloys containing shearable θ'' precipitates

The critical resolved shear stress of an Al 4 wt. % Cu alloy containing a homogeneous distribution of theta'' precipitates was determined by means of dislocation dynamics simulations. The size distribution, shape, orientation and volume fraction of the precipitates in the alloy were obtained from transmission electron microscopy observations while the parameters controlling the dislocation/precipitate interactions (elastic mismatch, transformation strains, dislocation mobility and cross-slip probability, etc.) were calculated from atomistic simulations. The precipitates were assumed to be either impenetrable or shearable by the dislocations, the latter characterized by a threshold shear stress that has to be overcome to shear the precipitate. The predictions of the simulations in terms of the critical resolved shear stress and of the dislocation/precipitate interaction mechanisms were in good agreement with the experimental results. It was concluded that the optimum strength of this alloy is attained with a homogeneous distribution of theta'' precipitates whose average size (approximate to 40 nm) is at the transition between precipitate shearing and looping. Overall, the dislocation dynamics strategy presented in this paper is able to provide quantitative predictions of precipitate strengthening in metallic alloys.

Automated summary

Dislocation dynamics simulations were used to determine the critical resolved shear stress of an Al 4 wt. % Cu alloy containing theta'' precipitates, with results in good agreement with experimental data. The optimal strength of the alloy was found to be achieved with a homogeneous distribution of theta'' precipitates at an average size transitional between shearing and looping. Overall, the strategy presented in this study provides quantitative predictions of precipitate strengthening in metallic alloys.