Insights into Temperature and Strain Rate Dependent Deformation Behaviors of BCC Fe from Discrete Dislocation Dynamics Simulations

Despite the promising prospects of body-centered cubic iron (BCC Fe) in aerospace, energy transportation, and nuclear applications, the effects of extreme environments on its mechanical behaviors and deformation mechanisms remain elusive to date. In this work, the mechanical responses and deformation behaviors of BCC Fe single crystals under extreme loading conditions are investigated by performing the three-dimensional discrete dislocation dynamics simulations. It turns out that the yield strength (σ_y) of BCC Fe can be enhanced by increasing the strain rate (ε˙) and/or decreasing the deformation temperature (T). With the strain rate increasing from ε˙= 10² s⁻¹ to 10⁶ s⁻¹, the yield strength at 300 K rises from σ_y = 51.14 MPa to 1114.57 MPa. When the strain rate exceeds 10³ s⁻¹, an elastic overshoot phenomenon appears because the applied stress and the low initial dislocation density at the early tensile stage cannot drive the plastic deformation immediately. With the temperature increasing from T = 100 K to 800 K, the yield strength at ε˙= 10³ s⁻¹ decreases from σ_y = 64.97 MPa to 59.50 MPa. Such temperature and strain rate sensitivity of deformation behaviors are clarified from variations in the configurations of dislocation evolution and dislocation density fluxes. It is demonstrated that at low strain rate (ε˙≤ 10³ s⁻¹) conditions, the deformation behaviors of BCC Fe are dominated by the dislocation multi-slip mechanism. With increasing strain rate to e.g., ε˙> 10³ s⁻¹, the deformation behaviors are governed by the dislocation single-slip. Our investigation on the temperature and strain rate sensitivity of deformation behaviors provides insightful guidance for optimizing the mechanical performances of BCC Fe based ferritic steels.