Atomistic Simulations of Growth Mechanisms of Hydrogen Blisters in Copper

Blistering is a process that is observed near the surfaces of metals exposed to prolonged irradiation by gaseous ions, as iin radio-frequency quadrupoles accelerating structures.<br/>The mechanism of continuous growth of a small bubble to a quantifiable size blister is not completely understood. Frequently, such procress is associated with the prismatic dislocation loop punching, which takes place at very short timescales and cannot be covered by experimental techniques. In FCC metals, the pressurized gas within the voids easily causes emission of shear loops due to low stacking fault energy. These were suggested to provide explanation to the plastic growth of the bubbles. However, the detachment of such loops has not been demonstrated.<br/>We use molecular dynamics to address the fast bubble growth in Cu, associated with blistering, when exposed to H^- irradiation. To do that, we employ a methodology which allows us to closely follow the formation of prismatic loops with different H concentrations. We also analyze the interaction of these loops with surfaces of different crystallographic orientations. This study sheds light on the mechanism of blister formation and, also, to its effect on the surface exposed to irradia<br/>We observe the emission of a complete prismatic loop enclosed within several shear loops with Burgers vectors aligned with the gliding direction of the prismatic loop. We show that the prismatic loops are not necessarily smaller than the bubble cross-section. In addition to this, we note that these loops travel toward defects-sinks such as grain boundaries or surfaces, and in the latter case, are creating different shape protrusions. These protrusions' shapes are different depending on the grain orientation, as observed experimentally, and we verify it by our computational method.<br/>In this work, we present the mechanisms of prismatic loop punching and the dislocations-surface interactions, which are essential to predict the behavior and to design the accelerating devices.