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 /-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 -800 mV_(SCE) (E_A, vs saturated calomel) and lower. Intergranular cracking is eliminated by reduced cathodic polarization more positive than —750 mV_(SCE). Crack tip diffusible H concentration rises, from near 0 wppm at E_A of —765 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.
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