Atomistic investigation of dislocation mechanism in orientation effect of θ′ precipitates in the stress-aged Al-Cu single crystal

JJ Li and G Li and Y Gao and H Zhou and SP Zhang and XB Guo, JOURNAL OF CENTRAL SOUTH UNIVERSITY, 32, 789-805 (2025).

DOI: 10.1007/s11771-025-5903-9

The orientation effect of theta ' precipitates in stress-aged Al-Cu alloys has ambiguous interpretations. One view is that theta ' precipitates prefer to grow on the habit planes perpendicular to the applied compressive stress, while the other view suggests growth on habit planes parallel to the applied stress. In this study, stress-aged Al-4 wt.%Cu single crystal was sampled from three different <100>(Al) zone axes to observe the distribution of theta ' precipitates. A hybrid Monte-Carlo/molecular dynamics simulations were used to investigate the orientation effect of theta ' precipitates. The simulation results are consistent with experimental observations and indicate that theta ' precipitates prefer to grow on the habit planes that are parallel to the direction of the applied compressive stress, not along the planes perpendicular to it. It is also found that 1/2<110> perfect dislocations are generated as theta ' precipitates plates grow thicker, and the reaction of 1/2<110> perfect dislocations decomposing into 1/6<112> Shockley dislocations lead to an increase in the length of theta ' precipitates. The former does not enhance the orientation effect, whereas the latter leads to a more significant orientation effect. Additionally, the degree of the orientation effect of theta ' precipitates is determined by the reduction of 1/2<110> dislocations with a positive correlation between them.

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