Calculation of internal stresses around Cu precipitates in the bcc Fe matrix by atomic simulation

Abstract

In order to better understand the effect of fine Cu precipitates on the mechanical properties of body-centred-cubic (bcc) Fe, atomic simulations of bcc Fe with bcc Cu precipitates under mechanical loading were conducted by using the molecular dynamics (MD) method in conjunction with embedded atom method (EAM) potentials. The atomic configurations showed that all bcc Cu precipitates in bcc Fe matrices have the transformation tendency from bcc to 9R in the absence of external loading. When compressive stresses were loaded and reached a critical value, the transformation from bcc to the 9R variant occurred inside Cu precipitates, and these transformed Cu precipitates resulted in structure changes of matrix Fe. On the other hand, this kind of transformation did not take place under tensile stress. The corresponding internal stress fields around the distorted and transformed Cu precipitates were evaluated. It was found that the resolved shear stresses of the internal stress field on the main slip systems of bcc Fe are of the same order of magnitude as the yield stress of perfect single crystal Fe. This may affect the dislocation slip and contribute to material hardening.