Abstract
IN718 is a widely used nickel-based superalloy with high strength and corrosion resistance. However, numerous works have shown that IN718 may be susceptible to hydrogen embrittlement. Many questions on its mechanical behavior in gaseous hydrogen environments especially at very low temperature are not answered yet. Further investigations are necessary to ensure the operational safety of components in contact with hydrogen under relevant operating conditions.
Different methods for testing with hydrogen are available. A common one is testing in an autoclave with gaseous hydrogen atmosphere which is expensive and is mostly limited to room temperature. In this study the tubular specimen technique is used as it allows to test with in-situ hydrogen charging at a wide range of temperatures. In this technique, a hole is drilled through a specimen and filled with pressurized hydrogen gas. Since hydrogen effects are strongly dependent on temperature, the low cycle fatigue behavior of IN718 under in-situ hydrogen charging at room temperature and in a liquid nitrogen bath at 77 K is under investigation. The investigations were specifically addressing material deposited by an Additive Manufacturing method (Selective Laser Melting) to assess its properties. The influence of specimen geometry is investigated in finite element simulations. Results on the fatigue behavior of IN718 on tubular and conventional specimen are compared and the effects of hydrogen and temperature are discussed and interpreted.