Criteria for hydrogen-assisted crack initiation in Ni-based superalloy 718

Abstract

The tensile mechanical properties of a Ni-based superalloy 718 uniformly precharged with ≈ 90 mass ppm hydrogen were investigated under a wide range of temperatures to shed light on the long-standing uncertainties surrounding the H-related embrittlement mechanisms of the material. The detrimental effect of H on ductility was found to be substantial in the near-ambient to high-temperature range, up to 300 °C, stemming from H-assisted microcrack initiations along annealing twin boundaries (ATBs) and crystallographic slip planes (SPs). Dynamic H-dislocation interaction, which has been thought to be a prerequisite for the onset of embrittlement, was found to be unimportant, as demonstrated by employing supplemental tests that incorporated prestraining and intermediate temperature changes. By combining the insights gained from the successfully designed test program, a new model for the nucleation process of H-induced fracturing was established.