A chraf Radi

UTC, Compiègne, France & ENSMA, Poitiers, France



Nickel-based superalloys are known for their excellent mechanical strength, especially in fatigue, as well as for their good resistance to corrosion and oxidation. However, when these materials are exposed to hydrogen, their cyclic response may be altered, which can lead to premature damage under hydrogen's effect (HE: hydrogen embrittlement). Many mechanisms have been proposed to describe hydrogen embrittlement, with the most commonly cited being hydrogen enhanced localized plasticity (HELP), hydrogen-enhanced decohesion (HEDE), and adsorption-induced dislocation emission (AIDE) [1]. Additionally, a wide variety of previous research has identified that hydrogen modifies the elementary processes associated with plasticity. However, some questions remain about the antagonist effects of hardening and softening induced by hydrogen on cyclic stress-strain behavior in the case of nickel-based alloys with a given precipitation state. In the present work, the impact of hydrogen on the fatigue behavior of a nickel-based superalloy (Waspaloy) was studied at room temperature in relation to the precipitation state in the underaged domain, where plasticity is localized and precipitates are shearable. For this, two precipitation states (HT0 and HT4) were considered for a constant grain size of 100 μm and varying precipitate sizes, d= 10nm and d= 30nm respectively. The two states were cathodically precharged with hydrogen, and then their cyclic behavior was compared to that of uncharged states. Internal stresses were evaluated using Cottrell-Dickson partitioning of hysteresis loops [2-3]. For these two microstructural configurations, it was found that hydrogen induced a mechanical softening in relation to the specific evolution of back stress and the effective stress. The relation between internal stresses, the dislocation structures and the extrusion heights of slip bands characterized respectively using TEM and AFM, is analyzed in order to account for the observed softening.


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