Dislocation Emission Model of Kinked Cracks in Aluminum Crystal under the Condition of Hydrogen Filling

Abstract

Based on the method of continuous distribution of dislocations and relevant theories of fracture mechanics, the effect of the distribution of hydrogen atoms at the crack tip (CT) on the emission of dislocations from kinked cracks under far-field uniform tensile stress is studied. The results show that hydrogen atoms can promote the emission and migration of CT dislocation, which leads to the increase of dislocation density (severe dislocation plugging), the increase of energy release rate, and the decrease of elastic zone size (dislocation-free zone) at CT. In addition, the sequence of initiation of grain boundary (GB) microcracks caused by dislocation emission at both ends of the whole crack (horizontal section and kinked section) and the propagation mechanism of a crack in a kinked section are analyzed. The results show that the critical tensile stress of GB microcrack initiation decreases with the increase of hydrogen atom radius rh and the decrease of hydrogen atom position xh, indicating that hydrogen atoms promote the initiation of GB microcrack initiation. At the same time, the existence of hydrogen atoms not only promotes the initiation of GB microcrack, but also accelerates the expansion of kinked cracks, which may eventually lead to the convergence of the main crack and the microcrack, resulting in the failure and destruction of materials. Therefore, the theoretical research in this paper has made a new understanding of the mechanism of hydrogen fracture of crystal materials. In this paper, the effects of hydrogen atoms at CT on dislocation emission at CT, crack initiation at GB, and the size of the dislocation-free zone were studied by establishing a crack dislocation model and using the distributed dislocation method. The results show that the accumulation of hydrogen atoms at the CT promotes the emission of dislocation at the CT, leads to the serious plugging of dislocation near the GB, promotes the initiation of microcracks and the expansion of kinked cracks, and leads to the reduction of the size of the dislocation-free zone at the CT. This work provides new information on the microscopic fracture mechanics of hydrogen on materials. On the one hand, it can better predict and prevent the fracture of materials, so as to improve the safety of engineering structures. On the other hand, it can help explain some microscopic experimental phenomena.