Mechanism of hydrogen embrittlement in a gamma-prime phase strengthened Fe–Ni based austenitic alloy

The mechanism of hydrogen embrittlement (HE) in a γ′-Ni3(Al,Ti) phase strengthened Fe–Ni based austenitic alloy has been investigated in detail. Hot hydrogen charging experiment and tensile test reveal that the alloy with coherent γ′ phase exhibits a much higher decrease in reduction of area (RA) than that of the alloy in the solution-treated state. However, three-dimensional atom probe (3DAP) experiment shows that segregation of hydrogen atoms is not found at the coherent interface between the γ′ phase and the matrix, which indicates that the interface is not a strong hydrogen trap. Furthermore, high-resolution transmission electron microscopy (TEM) observation indicates that the interface coherency is maintained during the deformation, even tensile to fracture. It is found that macroscale slip band rupture and intergranular fracture are promoted by serious dislocation planar slip, which become the predominant features in the tensile-to-fracture sample after hydrogen charging. This phenomenon has been interpreted as a result of combined effects of the γ′ phase and hydrogen in the precipitation-strengthened Fe–Ni based austenitic alloy.