First-Principle Calculation Of Mechanical Properties Of Impurity-Segregated FCC-Fe Grain Boundary

In nature,hydrogen atoms easily get into metal materials.Metal materials tend to crack along the crystal under service conditions in the hydrogen environment,which reduces the mechanical properties of metal materials,so brittle fracture occurs,also known as hydrogen embrittlement.At present,the mechanism of hydrogen atoms promotes the cracking of grain boundary to reduce the plasticity of materials is still unclear.So it has important guiding significance for preventing hydrogen-induced intergranular cracking and developing anti-hydrogen embrittlement materials to reveal the hydrogen-induced grain boundary embrittlement mechanism from the atomic scale.In this paper,we adopt the first-principles tensile test calculations to investigate the effect of hydrogen atom on the tensile deformation behavior of grain boundaries and reveal the mechanism of hydrogen atom induced grain boundary embrittlement.It is considered that the main reason for the embrittlement of grain boundary caused by hydrogen atom is that the hydrogen atom attracts the electrons of the neighboring iron atom,which reduces the electron density between the iron atoms,weakens the bond cooperation,and thus reduces the binding force of grain boundary.Finally,we investigate the response of grain boundaries under tensile strain conditions with chromium and hydrogen atoms segregated and discussed the effect of chromium atom on hydrogen-induced grain boundary cracking.When chromium and hydrogen atoms exist at the same time,the hydrogen atoms attract the electrons around the neighboring iron atoms during the grain boundary segregation,which makes the electron density and interaction force between Fe-Fe decrease.However,the strong bond and interaction between chromium atom and adjacent iron atom further weaken the Fe-Fe bond at the grain boundary and accelerate the decrease of the binding force at the grain boundary.With the increase of strain,the Fe-Fe bond breaks and the interaction force between Fe atoms and Cr atoms weakens gradually,which is not enough to compensate the local stress caused by the fracture of Fe bond and the fracture occurs at the grain boundary.Therefore,the co-segregation of chromium and hydrogen causes the intergranular stress Fracture occurs ahead of time.