The Effect of Additive Manufacturing Process Parameters on the Fatigue Performance of Alloy 718 in Elevated Pressure and Elevated Temperature Hydrogen Gas

The fatigue crack growth rates of wrought alloy 718 in the presence of high pressure hydrogen gas have been studied extensively; however, only limited studies have been performed on additively manufactured (AM) alloy 718 in hydrogen gas environments. AM processing parameters and post-processing heat treatment alter the microstructure and metallurgical features of the built material, which in turn influence the susceptibility to hydrogen embrittlement. Optimal processing parameters can be determined to minimize the material’s susceptibility to hydrogen embrittlement by correlating AM processing parameters to resultant metallurgical features, mechanical properties, and post-mortem damage morphologies. Additionally, the effect of test temperature on the fatigue crack growth rates and failure modes of the material was investigated at test temperatures up to 500F. The objectives of this study are to measure the fatigue crack growth rates of AM alloy 718 in gaseous hydrogen and elucidate the influence of the environment and microstructure on the hydrogen embrittlement susceptibility of AM alloy 718 by correlating mechanical performance to metallurgical features. Wrought 718 was similarly evaluated as a baseline material.