Parts made via additive manufacturing (AM) are being adopted broadly among many industries and used in an array of applications. AM parts are attractive to these industries for several reasons. Complex geometries that otherwise cannot be manufactured using traditional methods can be printed. Also, the ability to use AM to produce parts mitigates the need to maintain an inventory of replacement parts and avoids lengthy delivery times. Alloy 718 is widely used in demanding applications due to its high strength at high temperatures and excellent creep and corrosion resistance. Parts and components of this alloy can be created using AM techniques. However, in hydrogen and hydrogen-producing environments, alloy 718 is susceptible to hydrogen embrittlement (HE). The overall objective of this research program was to understand the underlying mechanisms governing the susceptibility of AM alloy 718 to HE by investigating the mechanical performance in high-pressure gaseous hydrogen and examining the microstructure to compare the wrought and AM materials. The fatigue crack growth rate tests showed that the wrought and all additively manufactured specimens had very similar mechanical response. Testing in gaseous hydrogen demonstrated that the AM and wrought materials had accelerated crack growth rates in the hydrogen gas environment; however, the effects of hydrogen were more pronounced in some materials than others. Metallurgical characterizations revealed differences in precipitates and metallurgy, and the post-test fracture surface examinations showed similar fracture morphology for all materials. No metallurgical feature or fracture morphology could be correlated with the more dramatic effects of hydrogen on the fatigue crack growth rates when comparing AM configurations and the wrought material.
Parts produced via additive manufacturing (AM) are being adopted broadly among many industries and used in an array of applications. AM parts are attractive to these industries for several reasons. Complex geometries that cannot be manufactured using traditional, subtractive methods can be produced additively. Also, the ability to use AM to produce parts mitigates the need to maintain an inventory of replacement parts because they can be readily produced on an as-needed basis, dramatically changing the supply chain. AM alloy 718 is of specific interest due to the alloy's excellent mechanical and corrosion properties over a wide range of service temperatures and environmental conditions. However, alloy 718 is susceptible to hydrogen embrittlement (HE) when exposed to gaseous hydrogen or hydrogen-producing environments such as spacecraft propulsion systems, machinery for hydrogen gas energy applications, downhole environments with presence of hydrogen sulfide, and in subsea applications where cathodic protection is used to mitigate corrosion. Microstructure characterization and mechanical properties of AM alloy 718 are reported in the literature1,2. However, the performance of AM alloy 718 in gaseous hydrogen and hydrogen-producing environments has not been thoroughly investigated and the effects of AM on the potential for HE have not been explored.
