Molecular dynamics study on the effect of hydrogen on the plastic behavior of α-Fe crack tip

Abstract

In this paper, the unilateral tension of α-Fe in the local region of the crack tip are simulated by molecular dynamics method, the plastic deformation behaviors and hydrogen embrittlement mechanism of the crack tip under different hydrogen concentration and hydrogen positions are analyzed. The results show that for the hydrogen-containing models, there exists a critical hydrogen concentration c0 that can make the plasticity of the α-Fe material reduce greatly. For the crack-free model, the main hydrogen embrittlement mechanism is adsorption-induced dislocation emission (AIDE), and the critical hydrogen concentration c0 is 0.3%. When the hydrogen concentration cH<c0, the plastic deformation mechanism is mainly dominated by phase transformation; when cH≥c0, the plastic deformation mechanism is phase transformation at low strains and dislocation motion at high strains. For the cracked model, the main mechanism of hydrogen embrittlement is hydrogen-enhanced local plasticity at the crack tip, with a critical c0 of 1.7%. When cH<c0, the plastic deformation mechanism of the model is a combination of phase transformation and dislocation; when cH≥c0, the plastic deformation mechanism is controlled by phase transformation. When the hydrogen is far away from the crack tip, the local mechanical behavior of the crack tip does not change significantly, while when hydrogen gathered at the crack tip, the addition of a small amount of hydrogen atoms will make the fracture strain decrease rapidly, which shows a mechanism of hydrogen-enhanced strain-induced vacancies (HESIV). A saturation value of hydrogen concentration at the crack tip is confirmed in this paper, when the local hydrogen concentration exceeds this saturation value, the plastic behaviour tends to be stable. The influence of hydrogen atoms distribution on the crack initiation behavior was determined by atomic configuration analysis.