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>The effect of aqueous phase inhibitors on mitigating potential-dependent hydrogen environments assisted cracking of an ultra-high strength steel.
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The effect of aqueous phase inhibitors on mitigating potential-dependent hydrogen environments assisted cracking of an ultra-high strength steel.
Low alloy ultra-high strength alloy steel (UHSS) suffer from hydrogen environment assisted cracking (HEAC) limiting their use in marine environments. Minimum HEAC susceptibility is observed at intermediate potentials. Models explain this by a reduction in crack tip diffusible hydrogen concentration (CH,diff), enhancing threshold stress intensity (KTH) and reducing stage-II crack growth rate (da/dtII). This research seeks to extend the reduced HEAC susceptibility region by reducing C H,diff using aqueous-phase inhibitors.;A multi-facetted approach was used to quantitatively study the effect of inhibitors on reducing CH,diff. Initial tests were conducted on planar electrodes in molybdate solutions at anodic potentials and in cerium solutions at cathodic potentials; however, rescaled crevices of larger dimensions were used to measure local potential and pH as a function of applied potentials and crevice dimensions. H-uptake models were used to predict local C H,diff as a function of local potential, pH and scaling factor in the anodic and cathodic tests. Micro-mechanical models were used to predict the effects of inhibition on HEAC susceptibility. Results were related to real-size cracks using scaling factors. Last, fracture experiments were undertaken to verify predicted KTH and da/dtII obtained from the integrated investigation approach.;The addition of molybdate reduced da/dtII to 1 nm/s, expanding the reduced HEAC region to more anodic potentials. The enhanced mitigation was possibly due to forming a surface film more resistant to crack tip dissolution in addition to molybdate-induced chemical buffering of acidification both leading to reduced CH,diff. The addition of cerium reduced da/dt II to 9 and 32 nm/s at etaH = -0.35 and -0.47 V, respectively, compared to 50 and 500 nm/s at similar cathodic conditions in uninhibited tests. Cerium chemically forms an insoluble film that can reduce CH,diff by reducing hydrogen absorption, enhancing hydrogen desorption, and/or enhancing hydrogen recombination.;The main scientific contribution is to interpret the effects of different inhibitors through the study of CH,diff and provide a protocol to computationally predict the effects of inhibitors on HEAC susceptibility with limited experiments. The engineering contribution is to identify two inhibitors, one cationic and one anionic, that can be delivered to crack tips from coatings to inhibit HEAC.
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