Hydrogen-assisted fatigue crack-propagation in a Ni-based superalloy 718, revealed via crack-path crystallography and deformation microstructures

Antagonistic fatigue crack propagation in Ni-based superalloy 718 under hydrogen-supply: Acceleration and deceleration phenomena

“…As can be discerned by the plane trace analysis, the crack insistently propagated through ATBs or {111} SPs. The propensity that the ATBs or {111} SPs are preferential crack paths in the CG coincided with the results at high-stress intensities such as ΔK = 30 or 50 MPa m 1/2 , given by a previous study by the authors 7 . For instance, as exhibited in Fig.…”

“…It has been represented that, as ΔK increased, the FCG acceleration became more pronounced, even with no acceleration below ΔK ≈ 30 MPa m 1/2 . At a higher ΔK regime, e.g., ΔK ≈ 50 MPa m 1/2 , time-dependent "static" crack growth emerged similarly to δ-FG in the present study by which the secondary cracks originated at the intersections of dislocation slip bands (DSBs) autocatalytically coalesced with the primary crack 7 . It is quite likely that the maximum stress intensity was not beyond the aforementioned resistance to the H-assisted cracking (K IH ) at ΔK < 30 MPa m 1/2 (K max < 33 MPa m 1/2 for R = 0.1) in the present study, then the FCG event exhibited "cycle-by-cycle" and "strain-controlled" crack propagation.…”

“…Ni-based superalloy 718 (Alloy718) displays superior mechanical properties: high-temperature performance combined with excellent strength-ductility balance, thereby utilized with the view to having better durability even in harsh environments, e.g., hydrogenating environment, oil well pipes, and rocket engines. Metallic materials exposed to hydrogen (H) exhibit their degradation in mechanical properties, including ductility 1,2 , fracture toughness [3][4][5][6] , and fatigue crack growth 7,8 , etc., widely called "hydrogen embrittlement (HE)" reported rstly by Johnson 9 . In particular, Alloy718 is extremely susceptible to HE 10 despite its notable superiorities.…”

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

“…Ni-based superalloy 718 (Alloy718) displays superior mechanical properties: high-temperature performance combined with excellent strength-ductility balance, thereby utilized with the view to having better durability even in harsh environments, e.g., hydrogenating environment, oil well pipes, and rocket engines. Metallic materials exposed to hydrogen (H) exhibit their degradation in mechanical properties, including ductility 1 , 2 , fracture toughness 3 – 6 , and fatigue crack growth 7 , 8 , etc., widely called “hydrogen embrittlement (HE)” reported firstly by Johnson 9 . In particular, Alloy718 is extremely susceptible to HE 10 despite its notable superiorities.…”

Hydrogen‐assisted fatigue crack propagation behavior of equiatomic Co–Cr–Fe–Mn–Ni high‐entropy alloy

“…[1][2][3] For instance, the obvious effect of hydrogen on materials' mechanical properties is a particularly severe increase of fatigue crack propagation rate, namely, hydrogen-assisted fatigue crack growth (HAFCG). [4][5][6][7] It is widely accepted from the recent decade studies that the failure modes can be ascribed to the intrinsic deformation mechanisms. For instance, locally dissolved hydrogen could enhance the mobility and velocity of dislocations, namely, the hydrogen-enhanced localized plasticity (HELP) model.…”