First Principles Study On Structure And Properties Of Fe-mn Alloy

TWIP(Twinning Induced Plasticity)steel is obtained by adding alloying elements on Fe-Mn alloy.By controlling the stacking fault energy of the steel,the twinning induced plasticity effect is controlled during the deformation process,so that the steel can obtain high strength and high plasticity at the same time.The research on TWIP steel and Fe-Mn alloy have mostly focused on the experimental field.However,there are no reports on the effect of alloying elements on TWIP steel matrix at atomic and electronic level.In this paper,the effects of Mn,Cr and Ni on γ-Fe were calculated by density functional theory.The characteristics of the Fe-Mn alloys were revealed.The influence of Al and C elements on the fault energy of the Fe-Mn alloys were calculated.The effects of alloying elements on electronic structure and crystal parameters were analyzed by energy band theory.The effects of alloying elements on the mechanical properties of the Fe-Mn alloys were investigated by stress-strain method.The influence law and mechanism of alloying elements were analyzed.There provided a basis for the composition design and theoretical research of steel.The results showed that the layer fault energy of Fe-Mn alloys decreased first and then increased with the content of Mn increasing.And the total energy of the system was reduced and the alloy structure was stabilized.Cr element reduced the layer fault energy as well as the total energy of the system.Ni element increased the layer fault energy and the total energy of the system.C element increased the layer fault energy of Fe-25 Mn alloy and the stability of alloy structure.The high content of Al could effectively increase the layer fault energy of Fe-25 Mn alloy.But Al increased the total energy of alloy and could not stabilize austenite.The electron structure analysis showed that there were obvious pseudo-energy gaps in the electron state density of Fe-Mn alloy crystals,and the electron density of states was mainly contributed by the electrons of Mn-3d and Fe-3d orbitals.Therefore,there were metal bonds,covalent bonds and a few ionic bonds in Fe-Mn alloy.With the increase of C content,the pseudo energy gap of Fe-25Mn-xC alloy disappeared and the state density increased in the low energy level region,where the hybridization of electron orbital among the three elements were relatively strong.The Mn-C pair formed by C and Mn had a strengthening effect on the alloy.Al element contributed little to the state density of the alloy,but the increase of Al element content greatly promoted the electron hybridization between Fe-Mn,enhanced the binding capacity between the two elements,which could effectively enhance the strength and plasticity of the alloy.From the perspective of mechanical properties,the volume modulus,young’s modulus and shear modulus of Fe-Mn alloy were decreasing as the content of Mn increase.C element was added to the Fe-25 Mn alloy,and the results showed that the volume modulus,style modulus and shear modulus of the alloy increased with the increase of C content.The elastic constants of Fe-25Mn-0.7 C alloy varied the most,and the volume modulus and young’s modulus increased rapidly while the shear modulus did not change at all.However,the value of B/G that reflected the ductility of the alloy increased rapidly from 1.51 to 1.96.