The precipitation and growth of AgCl on silver in physiological NaCl solution were investigated. AgCl was found to form at bottom of scratches on the surface which may be the less effective sites for diffusion or the favorable sites for heterogeneous nucleation. Patches of silver chloride expanded laterally on the substrate until a continuous film formed. The ionic transport path through this newly formed continuous film was via spaces between AgCl patches. As the film grew, the spaces between AgCl patches closed and ion transport was primarily via micro-channels running through AgCl patches. The decrease of AgCl layer conductivity during film growth were attributed to the clogging of micro-channels or decrease in charge carrier concentration inside the micro-channels. Under thin AgCl layer, i.e. on the order of a micrometer, the dissolution of silver substrate was under mixed activation-Ohmic control. Under thick AgCl layer, i.e. on the order of tens of micrometers, the dissolution of silver substrate was mediated by the Ohmic resistance of AgCl layer.

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.

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