Effect of hydrogen on deformation behavior of Alloy 725 revealed by in-situ bi-crystalline micropillar compression test

Abstract

Nickel-based Alloy 725 bi-crystalline micropillars with different types of grain boundaries (GBs) were compressed in hydrogen-free and in-situ hydrogen-charged conditions to investigate the hydrogen effect on the deformation behavior of the selected GBs. In the presence of hydrogen, the compressive stresses on the micropillars increase regardless of the GB type. It was proposed that this hydrogen-induced hardening behavior is the synergistic effect of hydrogen-enhanced dislocation multiplication and interactions, the pinning effect of hydrogen on dislocation motion, and hydrogen-enhanced lattice friction. Transmission electron backscatter diffraction (t-EBSD) results demonstrate that both low-angle GBs and high-angle GBs can effectively suppress dislocation transmission through the GBs, resulting in dislocations pile up along the GBs in the hydrogen-charged condition. In contrast, this behavior was not observed in the micropillars with twin boundaries.