Gaseous Hydrogen Charging and Fatigue Testing on IN718

Abstract IN718 is a precipitation hardened nickel-based superalloy, which is well known for its high strength, good corrosion and creep resistance from low to high temperatures. It is therefore a popular material for numerous applications. Nevertheless, it is known that hydrogen can strongly affect the mechanical properties of IN718. Some questions still need to be clarified to ensure the safe use of components in a hydrogen environment. In this work, the hydrogen uptake in a gaseous hydrogen environment and tensile and fatigue properties of pre-charged IN718 were investigated. Specimen were charged at 350°C and 100 bar hydrogen pressure. It turned out, that saturation was reached after 10 days with a hydrogen content of about 27 wppm. Tensile tests showed a loss of elongation to failure and reduction of area for the pre-charged specimen. Hydrogen effects were also evident in the low cycle fatigue test. The cycles to failure were significantly reduced. Investigations of the fracture surfaces showed clear differences in crack growth of non-charged and pre-charged tensile and fatigue specimen.