Hydrogen diffusion and trapping in a precipitation-hardened nickel–copper–aluminum alloy Monel K-500 (UNS N05500)

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

“…[22,46] x crit reflects the interaction of crack tip tensile stress and H concentration gradient, and is of order 1 lm for high strength Ti, Fe, Al, and Ni-based alloys, [45] suggesting damage localization at the maximum in the crack tip r H distribution [47] or H-sensitive dislocation structure. [38,44] D H for H in aged Monel K-500 at 298 K (25°C) was reported to be 5 to 6 9 10 À11 cm 2 /s, [48] 1.5 to 1.9 9 10 À10 cm 2 /s, [24] and 9 9 10 À11 to 4 9 10 À10 cm 2 /s, [29] suggesting an upperbound da/dt II from Eq.…”

“…Equation [3] neglects H trapping at crack tip dislocation structure. [49,52,53] Research on H uptake and diffusion in Monel K-500, [29] extended in the present research, establishes the applied cathodic potential dependence of crack tip C H-Diff necessary to implement the models in Eqs. [1] through [3].…”

“…[13] HEAC in a precracked specimen is often dominated by H production and uptake on crack tip surfaces due to the short diffusion distance (~1 lm) to highly stressed FPZ damage sites. [13] However, long exposure time and reduced overpotential for H production at the crack tip [29] suggest that a boldsurface source of H must be considered for HEAC in Ni superalloys. A study of IN718 showed that the threshold stress intensity factor (K TH ) for HEAC in high pressure H 2 or acidified chloride decreased as a unique function of increasing concentration of H produced at the crack tip.…”

“…[13] Low strength solid solution Monel Alloy 400 was susceptible to IG and TG IHAC. [26,27] The severity of EAC in Monel K-500 in chloride solution increases with increasing cathodic polarization, [2,25,28] which increases the overpotential for H production from water reduction, thus increasing the amount of H. [29] Absorbed H migrates to the highly stressed-localized crack tip fracture process zone (FPZ) where damage nucleates. [13] HEAC in a precracked specimen is often dominated by H production and uptake on crack tip surfaces due to the short diffusion distance (~1 lm) to highly stressed FPZ damage sites.…”

“…[1] through [3]. [29] This approach was applied to model HEAC in ultra-high strength steels. [42,54] The objectives of this research are to: (1) enhance an accelerated fracture mechanics test method for HEAC in moderate strength alloys, [42,55] (2) quantitatively characterize the HEAC kinetics of aged Monel K-500 in aqueous chloride solution with cathodic polarization, (3) establish C Hr vs applied cathodic potential for Monel K-500, and (4) model the applied potential dependencies of K TH and da/dt II based on crack tip H uptake using Eqs.…”