First Principles Calculation Of Generalized Stacking Fault Energy Of FCC Fe-Mn-C Alloy

C and Mn is the two major alloying elements that significantly affect the stacking fault energy and control the mechanical properties of FCC-Fe based alloys.However,it is not clear how C,Mn,C-Mn couple and their local distribution affect the stacking fault energy of FCC Fe based alloys.In this paper,first principles method based on density functional theory(DFT)is used to investigate the effects of C,Mn contents and the positions of C and Mn atoms on generalized stacking fault energy(GSFE)of FCC-Fe based alloy supercell model.GSFE of Fe-Mn-C supercell model with different C and Mn contents is calculated.The interaction between C and Mn atoms in Fe-Mn-C supercell model was investigated.The effect of C-Mn couple on the dislocation and twinning behavior in Fe-Mn-C supercell model was analyzed.It is found that the distance between the stacking fault plane and the slip plane of C atom affects the stacking fault energy of Fe based alloy supercell model.The closer the stacking fault surface is to the slip surface of C atom,the greater the stable stacking fault energy is.When the stacking fault plane is located on the slip plane of C atom,the Fe-C supercell model will form a highly unstable structure in the process of stacking fault formation,which makes the gsfe of the model increase sharply.With the increase of C content,the gsfe of Fe-C supercell model increased significantly.Compared with the uniform distribution of C atoms,the segregation of C atoms increases the gsfe of the supercell model in the slip process,which means that the barrier to be overcome for the stacking fault to continue to grow increases and the formation of twins becomes difficult.The addition of Mn atom reduces the stacking fault energy of FCC-Fe based alloy supercell model,and with the increase of Mn content,the stacking fault energy further decreases.Especially when the stacking fault plane is located in two atomic layers near the position of Mn atom,the steady-state stacking fault energy is significantly reduced,resulting in the so-called Suzuki effect.In the Fe-Mn-C supercell model,there is a strong attraction between C and Mn atoms,which makes C and Mn atoms form a C-Mn couple.The stacking fault energy of Fe-x Mn-0.6C calculated by VCA method first decreases and then increases.The distribution of Mn atoms on the stacking fault plane of Fe-x Mn-0.6C supercell model has a great influence on the stacking fault energy.In the Fe-x Mn-0.6C supercell model,when there are a certain number of Mn atoms on the stacking fault surface,the increase of Mn content is beneficial to the twinning behavior of the Fe-x Mn-0.6C supercell model;but when the number of Mn atoms is too large,the Mn atoms near the stacking fault surface segregate,which increases the stacking fault energy of Fe-x Mn-0.6C,and decreases the unstable stacking fault energy and the unstable twin stacking fault energy,which is not conducive to the generation of twins in the Fe-x Mn-0.6C supercell model.Compared with the unpaired case of C and Mn,the formation of C-Mn couple leads to the increase of stacking fault energy of Fe-Mn-C supercell model.In addition,with the increase of C content,the number of C atoms and the number of C-Mn couple increase,leading to the further increase of stacking fault energy in the supercell model,which indicates that increasing C content can inhibit the formation of stacking faults and the growth of twins.