Effects of Temperature, Pressure and Frequency on Low Cycle Fatigue of Alloy 718 under Gaseous Hydrogen

The development of a climate-neutral hydrogen economy raises many questions regarding the use of numerous components and materials in direct contact with hydrogen, as hydrogen can deteriorate the mechanical properties of metals. A high testing effort is therefore necessary to qualify the components for safe use. The operating conditions of components in hydrogen atmosphere reach over a wide range of pressures and temperatures, as well as static and dynamic loads which expands the test field enormously. There are only a few of the cost-intensive autoclave test benches worldwide commonly used for testing under a high-pressure gaseous hydrogen atmosphere. A simple alternative testing technique is the hollow specimen technique, in which an axial hole is introduced into the specimen and filled with hydrogen gas during the experiment. With this test method, the specimen can also be easily temperature-controlled from the outside using liquid nitrogen or an induction heater. The hollow specimen technique was used to investigate the low-cycle fatigue behaviour of the nickel-based superalloy 718 under the influence of gaseous hydrogen. Comparative tests between hollow specimens and solid specimens were carried out to qualify the technique. Subsequently, influencing factors were investigated namely temperature (from -100 °C to 600 °C), pressure (from 10 bar to 250 bar) and frequency (from 0.001 Hz to 1 Hz) on the low-cycle fatigue behaviour under the influence of hydrogen. All 3 factors showed a significant influence on hydrogen damage.