Antagonistic fatigue crack acceleration/deceleration phenomena in Ni-based superalloy 718 under hydrogen-supply

Mechanical properties of structural alloys, including Ni-based superalloy 718 (Alloy718), are degraded when hydrogen (H) is supplied: hydrogen embrittlement (HE). The presence of H notably deteriorates fatigue crack growth (FCG) property, which renders the growth rate much higher and shortens the lifetime of the components operating in the hydrogenating environment. Hence, the mechanisms behind such acceleration phenomenon in FCG should be understood comprehensively toward developing promising alloys resistant to hydrogen occlusion. In particular, Alloy718 has a meager resistance to HE, even regularly displaying superior mechanical and physical performances. Notwithstanding, the present study unveiled that the FCG acceleration by dissolved H in Alloy718 can be negligible. An abnormal deceleration of FCG can instead be pronounced by optimizing the metallurgical state, a hopeful prospect in Ni-based alloys applied to the hydrogenating environment.

Automated summary

The mechanical properties of structural alloys, such as the Ni-based superalloy 718, are degraded by the presence of hydrogen, leading to hydrogen embrittlement. In particular, the fatigue crack growth (FCG) property is significantly deteriorated by hydrogen, resulting in a higher growth rate and shorter lifetime for components operating in a hydrogenating environment. Therefore, understanding the mechanisms behind this acceleration phenomenon is crucial for developing alloys that are resistant to hydrogen occlusion. This study reveals that the FCG acceleration in Alloy718 can be negligible when hydrogen is dissolved, and instead, an abnormal deceleration of FCG can be achieved by optimizing the metallurgical state, offering a hopeful prospect for Ni-based alloys in hydrogenating environments.