Hydrogen-enhanced intergranular failure of sulfur-doped nickel grain boundary: In situ electrochemical micro-cantilever bending vs. DFT

Abstract

Intergranular failure of nickel (Ni) single grain boundaries (GBs) owing to the segregation of sulfur (S), hydrogen (H), and their co-segregation has been investigated by employing micro-cantilever bending tests and density functional theory (DFT) calculations. A pure Ni GB shows completely plastic behavior with no fracture observed in the experiments. Electrochemical H-charging of the sample with no S present in the GB leads to a crack formed at the notch tip, which propagates by means of the mixed plastic–brittle fracture mode. Cantilever testing of the H-charged GB with S results in a clear brittle fracture of the GB. The co-segregation of S and H shifts the sudden drop in the load–displacement curves to smaller values of displacement. This is explained by the combined effect of these elements on the work of separation of the selected GB leading to severely decreased GB cohesion.