Atomistic Simulations Of Fracture And Hydrogen Embrittlement Of ?-Fe And The Effects Of Local Hydrogen Distribution

Due to the existence of atomic hydrogen,some catastrophic failures called hydrogen embrittlement(HE)often occur in iron and steels at low load and low hydrogen concentration during the manufacturing or service processes.HE is closely related to plastic phenomena affected by hydrogen,such as the interactions with dislocations and the accompanying martensitic transformations.However,the behavior of hydrogen is complicated and difficult to detect,especially for the sites and distributions which affect fractures,and the mechanism of HE still needs further studies.Atomistic simulations are widely used as they can observe the atomic behaviors in simulations.In this work,the fracture and HE of ?-Fe are studied by using several of them,and the influence of hydrogen distribution on HE process and hydrogen-induced hardening and softening are statistically analyzed.Firstly,we studied the mode I fracture and deformation-induced martensitic transformations(DIMT)of ?-Fe using the molecular dynamics(MD)method,and the observed transitions were verified by first principle calculations.A crack tip tracking algorithm is proposed,and based on which,the obtained critical stress intensity factor is proved to be close to the experimental results.The details of the DIMTs and the sources of the ? and ? phases were discussed.Then,the HE caused by the solute hydrogen was studied by MD,and the HE caused by hydrogen atoms adsorbed at the crack tip was studied by MD and time-stamped force-bias Monte Carlo method.The relationship between the crack velocity and the hydrogen distribution was studied statistically.The microvoid coalescence fracture caused by the adsorbed hydrogen atoms were analyzed.Finally,a high-throughput atomistic simulation is performed for the ?-Fe single crystal with interstitial solute hydrogen atoms,and the elastic constants and moduli were calculated.Then the effect of the microscopic distribution of hydrogen on elasticity was discussed in combination with the clustering algorithm,the influence of moduli,and hydrogen-induced hardening and softening.