Analysis of the influence of hydrogen on prismatic loops and dislocation dipole structure in an austenitic steel: Effect on stacking fault energy

The influence of hydrogen on crystal defects (point defects and dislocations) determines effects such as hydrogen-induced localized plasticity and damage. One of the structural variables controlling these effects is the stacking fault energy. Experimental and computational studies indicate that hydrogen reduces its value, thereby increasing the partial dislocation spacing, and influencing dislocation behavior. This study quantitatively investigates the influence of solute hydrogen (133 mass ppm) on prismatic loop and dislocation dipole structures in an austenitic steel by an approach based on scanning transmission electron microscopy (STEM) and anisotropic dislocation theory. The established method allows the estimation of the stacking fault energy with greater accuracy than approaches used in the literature. We show that hydrogen leads to several effects on crystal defects, increasing the average prismatic loop size and average dipole height of screw-type dipoles. The analysis of the dissociated dipole structure by a model based on anisotropic dislocation theory indicates that hydrogen reduces the stacking fault energy. We critically compare the present study with former reports in fcc materials and discuss the influence of hydrogen-charging conditions, imaging analysis method, and dislocation theory on the measurement of stacking fault energy. The effect of the present results on the deformation behavior is evaluated.