关键词: bcc Fe, 二元合金, 原子行位移能(ARD), 堆垛层错能(GSF), 固溶软化

Abstract: In this study, the mechanism of the solid solution softening (SSS) behavior in four binary alloys of bcc iron Fe-X (X= Cr, Co, Mo, W) at low temperatures and low concentrations was investigated using first-principles calculations. The SSS behavior of bcc Fe at low temperatures and low concentrations is controlled by the nucleation of double kinks. The intrinsic mechanism for SSS occurs when solute atoms directly reduce the nucleation energy barrier for the formation of double kinks. The extrinsic mechanism for SSS occurs when solute atoms reduce the number of interstice atoms, thereby reducing the nucleation energy barrier for double kinks. We calculated the atomic row displacement energy (ARD) and the generalized stacking fault energy (GSF) to clarify the SSS mechanism of the Fe-X (X= Cr, Co, Mo, W) binary alloys. The calculations showed that only Cr can slightly reduce the ARD and GSF energies, while Co, Mo, and W all cause an increase in the ARD and GSF energies. Therefore, according to the intrinsic mechanism of SSS, only Cr causes solid solution softening, while Co, Mo, and W all cause solid solution strengthening. Cr, Mo, and W interact with the surrounding Fe atoms in an antiferromagnetic manner, while Co interacts with Fe in a ferromagnetic manner. Although the ferromagnetic/antiferromagnetic interaction is somewhat correlated with the valence electron number and electron configuration, the nucleation energy barrier is not significantly correlated with them. Further calculations showed that there is a positive correlation between the nucleation energy barrier and the binding energy. The binding energy between Cr and Fe weakens, thus lowering the double kink nucleation energy barrier, while the binding energy between Co, Mo, W, and Fe strengthens, thus increasing the double kink nucleation energy barrier. However, the binding energy did not show a significant correlation with atomic radius or electron configuration, thus the nucleation energy barrier is not significantly correlated with these factors either. Considering the intrinsic mechanism, the increase in the binding energy between Co, Mo, W, and Fe causes the nucleation energy barrier for double kinks to increase, resulting in solid solution strengthening. Therefore, the SSS behavior of the Fe-based binary alloys with Co, Mo, and W at low temperature and low concentration cannot be explained by the intrinsic mechanism, and external mechanisms, such as the effects of interstitial C atoms, need to be considered. On the other hand, the solid solution softening behavior of Cr may be explained by the intrinsic mechanism.

Key words: bcc Fe, Binary alloy, Atomic row displacement(ARD), Generalized stacking fault energy(GSF), Solid solution softening