Influence of nanoscale Cu precipitates in $\alpha \text{-Fe}$ on dislocation core structure and strengthening

Atomistic simulations of the interaction of a screw dislocation in $\alpha \text{-Fe}$ with different size bcc Cu precipitates suggest two plausible strengthening mechanisms. For precipitate diameters in the range $1.5\text{nm}\le d\le 3.3\text{nm}$, the dislocation core structure within the Cu precipitate undergoes a polarized to nonpolarized transformation, leading to the dislocation pinning at the precipitate-matrix interface and the bowing out of the dislocation line. The calculated bow-out angle and resolved shear stress required to detach the dislocation from the precipitate are in agreement with recent experiments. The structural transition of larger $\left(d\ge 3.3\text{nm}\right)$ Cu precipitates under high shear stress is responsible for the loss of slip systems and hence for dislocation pinning.

Figure 1

(Color online) Schematic geometry for the Cu precipitate denoted by green (light gray) interacting with the dislocation line denoted by red (dark gray) placed in the Fe host, where ${\sigma }_{xz}$ is the external applied stress.

Figure 2

(Color online) MD snapshots of the dislocation core interacting with the 1.0 nm Cu precipitate as the dislocation glides on the $\left(10\overline{1}\right)$ plane along the $\left[1\overline{2}1\right]$ direction under an external stress of 700 MPa at (a) 268 ps, (b) 274 ps, and (c) 290 ps, respectively. Green (light gray) and red (dark gray) circles represent Cu and Fe atoms, respectively.

Figure 3

(Color online) MD snapshots of the dislocation core interacting with the 2.3 nm Cu precipitate as the dislocation glides on the $\left(10\overline{1}\right)$ plane along the $\left[1\overline{2}1\right]$ direction at (a) 243 ps, (b) 272 ps, (c) 312 ps, and (d) 320 ps, respectively. Green (light gray) and red (dark gray) circles represent Cu and Fe atoms, respectively.

Figure 4

(Color online) DD maps for the dislocation core inside a Cu precipitate with (a) $d=2.3\text{nm}$; (b) $d=1.0\text{nm}$; and (c) $d=0.0\text{nm}$ (pure $\alpha \text{-Fe}$). The red (dark gray) and green (light gray) circles represent Fe and Cu atoms, respectively. (d) Change in dislocation core polarization versus atomic position [normalized to (b)] along the dislocation line. The black solid and red (dark gray) dashed curves correspond to the 2.3 and 1.0 nm Cu precipitates, respectively. The vertical dashed lines indicate the precipitate-matrix interface.

Figure 5

(Color online) DD maps of the dislocation core of the 2.3 nm Cu precipitate during the detachment process in Fig. 3c at (a) 280 ps, (b) 297 ps, (c) 303 ps, and (d) 315 ps. The red (dark gray) and green (light gray) circles represent Fe and Cu atoms, respectively. The dislocation glides along the $\left[1\overline{2}1\right]$ direction under an external stress of 1,000 MPa.

Figure 6

(Color online) MD snapshots of the dislocation core interacting with the 4.4 nm Cu precipitate as the dislocation initially glides along the $\left[1\overline{2}1\right]$ direction, at (a) 260 ps, (b) 330 ps, (c) 540 ps, (d) 722 ps, and (e) 725 ps. Green (light gray) and red (dark gray) circles represent Cu and Fe atoms, respectively.