Molecular Dynamics Simulation-based Study Of FeO/Fe Interface Fracture

Acid-free descaling process,it is extremely important to understand the fracture nature of the oxide scale in order to provide accurate process parameters for the acid-free descaling process.The dynamic evolution of the oxide scale microstructure under external loading is a key scientific issue in this research area.In this paper,we mainly use molecular dynamics simulations to study and analyze the micromechanical behaviors and physical mechanisms during the damage and destruction of single-crystal and polycrystalline FeO/Fe interfaces in the tensile state at the nanoscale,specifically.1.The dynamic process of single-crystal FeO/Fe interface fracture is studied from both global and local perspectives.The stress characteristics of the crack constant stage,the crack unsteady extension stage and the crack steady state extension stage are analyzed from the global perspective.The local positive stress distribution and displacement changes in the crack constant stage and crack extension stage were analyzed locally;and the local positive stress and displacement data under the crack steady-state extension condition were used to fit the traction separation curve plots,which were also compared with three models such as exponential,bilinear and cubic polynomial viscous cohesion models with the sum of squared deviations of 245.86,222.02 and 406.10,respectively.It shows that the simulation results are consistent with the bilinear cohesion model.2.The effects of pore radius and number on the crack expansion at the FeO/Fe interface under different porosity were analyzed from two perspectives of constant pore size and constant pore number.The effect of different porosity models on the interfacial stress was analyzed,and it was found that the weakening mechanism of the stress was different between the fixed pore size and fixed pore number models.In terms of interfacial crack extension,the dynamic instability of crack extension leads to the transition from brittle to ductile crack extension,which results in the asymmetry of crack extension,and the larger the porosity,the more obvious the asymmetry is.The porosity leads to a slowing down of the stress growth rate at the crack tip,and the porosity is inversely proportional to the stress growth rate.At 9% porosity,the interfacial crack shifts to pore development.3.The effect of FeO polycrystalline grain size on the fracture of polycrystalline FeO/Fe interface was studied.The results show that the static stress,shear stress,CSP and potential energy at the FeO grain boundaries are higher than those inside the crystal,and during the tensile process,defects preferentially form in the grain boundaries of FeO,expand along the grain boundaries,and eventually form fractures.In the interval of grain size from 4.0nm to 6.3 nm,the model exhibits a paradoxical Hall-Petch theorem,where the larger the grain size is,the better the mechanical properties are.Also,the angle between the crack expansion path and the force direction has a great influence on the expansion of grain boundaries.4.The effect of the location of hole defects within polycrystalline FeO on the fracture of the polycrystalline FeO/Fe interface was studied.The results show that the presence of hole defects makes the atoms around the holes subject to high tensile stresses,the CSP values of the atoms around the holes increase significantly,and the hole defects lead to a decrease in the material stress during the stretching process.Under tensile action,defects form at the grain boundaries of FeO polycrystals and develop along the grain boundaries to eventually fracture.The influence of hole defects on interfacial fracture is different at different locations,and the weakening of the interfacial model is from weak to strong in the order of intracrystalline,crystalline interface,and trigonal grain boundaries.