Measurement and Modeling of Hydrogen Environment-Assisted Cracking in Monel K-500

Abstract

Hydrogen environment-assisted cracking (HEAC) of Monel K-500 is quantified using slow-rising stress intensity loading with electrical potential monitoring of small crack propagation and elastoplastic J-integral analysis. For this loading, with concurrent crack tip plastic strain and H accumulation, aged Monel K-500 is susceptible to intergranular HEAC in NaCl solution when cathodically polarized at À800 mV SCE (E A , vs saturated calomel) and lower. Intergranular cracking is eliminated by reduced cathodic polarization more positive than À750 mV SCE . Crack tip diffusible H concentration rises, from near 0 wppm at E A of À765 mV SCE , with increasing cathodic polarization. This behavior is quantified by thermal desorption spectroscopy and barnacle cell measurements of hydrogen solubility vs overpotential for planar electrodes, plus measured-local crevice potential, and pH scaled to the crack tip. Using crack tip H concentration, excellent agreement is demonstrated between measurements and decohesion-based model predictions of the E A dependencies of threshold stress intensity and Stage II growth rate. A critical level of cathodic polarization must be exceeded for HEAC to occur in aged Monel K-500. The damaging-cathodic potential regime likely shifts more negative for quasi-static loading or increasing metallurgical resistance to HEAC.

The interaction of corrosion fatigue and stress-corrosion cracking in a precipitation-hardened martensitic stainless steel

“…This behavior leads to a false increase of the measured potential that the direct current potential difference (dcPD) method translates into an indication of crack extension. 37 This behavior is the basis of for the plotted resolution limit reported in Fig. 1, which was previously established using C465 and other UHSS data (Pioszak, G. Unpublished work, University of Virginia, 2013).…”

“…This similarity is consistent with a HE-based SCC mechanism, where crack growth in the Stage II regime is proposed to be rate limited by diffusion of H ahead of the crack tip. 37,[40][41][42] Specifically, if the HE-based SCC mechanism is controlling and if there is a constant crack-tip environment to set equivalent H production rates, then these equivalent growth rates would be expected due to constant diffusion rates in the crack-tip process zone. In toto, the IG fracture morphology, frequency dependence, and da/dt values strongly support a SCCbased mechanism governing the plateau behavior observed at low ΔK.…”

Strain Gradient Plasticity-Based Modeling of Damage and Fracture

“…Since results have been obtained for a load level (≈ 20 MPa √ m for a typical steel) that could be considered a lower bound for damage modeling (see e.g. [102]), accounting for the influence of GNDs close to the crack tip appears to be imperative in hydrogen embrittlement models.…”

“…Model assessment is based on detailed measurements of da/dt versus K I reported for HEAC in a Ni-Cu superalloy [102,171] and two ultra-high strength martensitic steels [92,172], each stressed in a chloride solution. Electrochemistry measurements and modeling yielded crack tip H concentration versus applied potential (E APP ) [102,173], as well as trap-affected effective hydrogen diffusivity (D H−EFF ) for each alloy [174][175][176].…”

“…Models adopting the hypothesis that interstitial hydrogen lowers the cohesive strength are able to capture the experimental trends depicted by high-strength steels in aqueous solutions and hydrogen-containing gaseous environments (see [36]). Several attractive hydrogen-sensitive cohesive zone formulations have been proposed within this HEDE framework (e.g., [123][124][125][126]); and accurate estimations of the threshold stress intensity K T H and the stage II subcritical crack growth rate have been obtained by means of the Gerberich et al [127] dislocation-based model [92,102,128]. However, uncertain adjustable parameters are a shortcoming of the models and it is necessary to better define conditions within 0.1-5 µm of the crack tip, where dislocations, microstructure and chemistry dominate material behavior [129].…”