The Effect Of Hydrogen Atom On Stacking Fault Energy Of Austenitic Steels And Hydrogen Diffusion Behavior

In nature,hydrogen can easily enter to metal materials,resulting a reduction in the mechanical properties of metal materials and inducing brittle failures,also known as hydrogen embrittlement.In industry,the failure of metal materials due to hydrogen embrittlement will cause significant property damage and life hazards.Therefore,the study of hydrogen embrittlement has always been a concern in the academic community.At present,many mechanisms have been proposed for hydrogen embrittlement mechanism,such as HP,HELP,HID,etc.However,different mechanisms all have certain limitations.Therefore,the exact mechanism of hydrogen embrittlement is still quite different in the academic community.Therefore,it is of great significance to study hydrogen embrittlement.Under the existing experimental conditions and methods,it is difficult to truly track the occurrence of hydrogen embrittlement.However,the use of first-principles calculations which based on density functional theory facilitates a fundamental understanding of the interaction between hydrogen and metal.Therefore,the first-principles calculation method was used to study the influence of hydrogen atoms on generalized stacking fault energy（GSFE）of FCC-Fe and its influencing mechanism.Secondly,the diffusion paths of hydrogen locate in FCC-Fe,HCP-Fe single phase andγ/ε was studied.And the diffusion coefficients of hydrogen atoms in the three structures were deduced according to the Arrhenius formula.（1）The stacking fault energy is an important parameter of the FCC metal deformation type.When H atom locate in the slip layer,the unstable SFE increases sharply,and the stable SFE also increases.When the concentration of hydrogen increases along the[112]direction,the GSFE curve（including stable and unstable SFE）increases significantly.When he concentration of hydrogen increases along the[111]direction,the unstable SFE does not change.The stable SFE increase.With the increase of unstable SFE,the nucleation of partial dislocations becomes harder which lead to material brittle.The C atom can significantly increase the FCC-Fe’s stable SFE.At the same time,when added the interstitial atoms B,C and the substitution atoms Mn,Cu,Ni and Cr can reduce the effect of hydrogen on the stable SFE.Compared to the binary system,hydrogen in the ternary system has a greater effect on the FCC-Fe SFE.By analyzing the charge density difference and the partial density of states（PDOS）,the hybrid conjugation exists between Fe atom and H atom,and then the H-Fe bond is formed,which weakening the interaction between Fe and Fe atoms,and finally affecting the GSFE curve.（2）For single-phase FCC-Fe and HCP-Fe,the optimal hydrogen occupancy is O-site,and the path of hydrogen diffusion is O-site to T-site to O-site,O-site to O-site,respectively.Finally get the diffusion coefficient of hydrogen in two single phases:D_FCC=3.22×10^-4 exp（-8425/T）cm²/s>D_HCP=6.161×10^-4 exp（-8830/T）cm²/s（3）The optimal hydrogen atom occupying at the γ/ε interface is the O-site in FCC-1（also known as the interface layer）.In the entire interface structure,hydrogen preferentially occupies the O-site,moreover,the energy of the hydrogen locate in the FCC phase is significantly lower than in the HCP phase.By calculating the Griffith’s fracture work at different O-site which used to evaluate the strength of interface.It is found that when hydrogen is not occupied in the interface layer,the interface Griffith work of fracture does not change,when hydrogen occupied in the interface,the Griffith s fracture work is greatly reduced,indicating that hydrogen reduces the strength of the γ/ε interface.By calculating the diffusion energy barriers near the interface,the results show that the diffusion paths are O-site to T-site to O-site in several layers near the interface layer.According to the Arrhenius formula,the diffusion coefficient of hydrogen at the interface structure is calculated as:D（T）=1.464×10^-4exp（-4193/T）cm²/s,it is much larger than the diffusion coefficient of hydrogen at the single phase of FCC and HCP.