Abnormal Strain Rate Sensitivity Driven by a Unit Dislocation-Obstacle Interaction in bcc Fe

The interaction between an edge dislocation and a sessile vacancy cluster in bcc Fe is investigated over a wide range of strain rates from ${10}^8$ down to ${10}^3{\mathrm{s}}^{-1}$, which is enabled by employing an energy landscape-based atomistic modeling algorithm. It is observed that, at low strain rates regime less than ${10}^5{\mathrm{s}}^{-1}$, such interaction leads to a surprising negative strain rate sensitivity behavior because of the different intermediate microstructures emerged under the complex interplays between thermal activation and applied strain rate. Implications of our findings regarding the previously established global diffusion model are also discussed.

Figure 1

Illustration for the dynamic model in capturing the dislocation-obstacle interaction as a function of strain rate $\dot{ϵ}$ and temperature $T$ after combining the autonomous basin climbing method and transition state theory.

Figure 2

(a) The stress-strain curve, and associated potential energy (per atom on average) of the system, during the static interaction. (b) Critical atomistic configurations during the static interaction as shown in (a). The atoms are visualized by Atomeye [20], and colored according to different coordinate numbers.

Figure 3

(a)–(b) The stress-strain curves for the dislocation void interaction under different strain rate conditions, provided by ABC-T and MD simulations, respectively. (c) The associated critical atomic configurations after the interaction.

Figure 4

The CRSS under different strain rate conditions. Red open squares are the results of ABC-T framework simulations, while the black squares represent the MD simulations results.

Figure 5

(a) The potential energy differences of the system under different strain rate conditions, with respect to the static energy curve. (b) The atomistic configurations during the interactions, at various strain rates. (c) The atom density distributions along the $x$ axis, i.e., the $⟨111⟩$ direction, for structures S1–S5. The vacancy cluster’s fractional coordinate along the $x$ axis is about 0.8. It clearly shows that for high strain rates ${10}^6$ and ${10}^8{\mathrm{s}}^{-1}$, the vacancy clusters are ripped into parts, while such behavior is not observed for lower strain rates.