A comparison of internal hydrogen embrittlement and hydrogen environment embrittlement of X-750

Abstract

Hydrogen has been shown to degrade the mechanical properties of nickel-base alloys. This degradation occurs whether the material is in a hydrogen producing environment or if the material has dissolved hydrogen in the metal due to prior exposure to hydrogen. Materials behave differently under these two conditions. Therefore, the degradation due to hydrogen has been split into two categories, internal hydrogen embrittlement (IHE) and hydrogen environment embrittlement (HEE). IHE may be defined as the embrittlement of a material that has been charged with hydrogen prior to testing or service while HEE may be defined by the embrittlement of a material in a hydrogen environment where the hydrogen may come from gaseous hydrogen or generated from a corrosion reaction. This work compares IHE and HEE of fracture mechanics specimens. Different fugacities of hydrogen for HEE and hydrogen concentrations for IHE were examined for alloy X-750, a nickel-base super alloy. The test results are analyzed and the role of hydrogen in IHE and HEE is evaluated. A model based on a critical grain boundary hydrogen concentration is proposed to describe the behavior in both HEE and IHE conditions.