Methodology for Hydrogen-Assisted Fatigue Testing Using In Situ Cathodic Charging

With hydrogen being a promising candidate for many future and current energy applications, there is a need for material-testing solutions, which can represent hydrogen charging under superimposed mechanical loading. Usage of high purity gaseous hydrogen under high pressure in commercial solutions entails huge costs and also potential safety concerns. Therefore, a setup was developed utilizing a customized electrochemical charging cell built into a dynamic testing system. With this setup, two heat treatment states of AISI 4140 (DIN 1.7225, 42CrMo4) with varying yield and ultimate tensile strength were characterized in constant amplitude tests. S-N (Woehler) curves differ between heat-treated states, and when comparing testing in air with in situ cathodic hydrogen-charged specimens, hydrogen proves to be detrimental to the material properties. For both states considered, the presence of hydrogen leads to a reduction in fatigue life. Fractographic analyses by scanning electron microscopy reveals that for in situ cathodic hydrogen-charged specimens, the crack initiation mechanisms change for the higher strength heat treatment state.