Denny A. Jones

A unified mechanism of stress corrosion and corrosion fatigue cracking

A mechanism of stress corrosion cracking (SCC) is outlined in which anodic dissolution at film rupture sites relieves strain hardening and reduces the fracture stress at the crack tip. Experimental evidence is cited to suggest that relief of strain hardening occurs by interaction of subsurface dislocations with divacancies generated by the anodic dissolution. A transgranular crack propagates by accumulation of divacancies on prismatic planes which then separate by cleavage under plane strain conditions at the crack tip. At appropriate metallurgical and chemical conditions, anodic dissolution and/or divacancy migration may be enhanced at grain boundaries, leading to an intergranular failure mode. Evidence is also available to indicate that cyclic loading relieves strain hardening. Relief of strain hardening by combined cyclic loading and corrosion accounts for the higher incidence of corrosion fatigue cracking (CFC) without the requirement of any critical dissolved species. Data on fatigue of stainless steel at elevated temperature in both vacuum and air provide additional support for the proposed mechanism.

Electrochemical Corrosion Studies on Zinc-Coated Steel

Abstract The polarization behavior of various pure zinc, Al-Zn, and Zn-Ni coatings was studied to evaluate electrochemical methods for use in testing the performance of such coatings on sheet steel...

Evaluation of Corrosive Degradation in Coated Steel Using Alternating Current Impedance Spectroscopy

Abstract Alternating current (AC) impedance spectroscopy was applied to measure the degradation of steel coatings previously exposed to corrosive solutions such as tap water and 3% sodium chloride ...

Polarization Studies of Brass-Steel Galvanic Couples

Abstract Electrochemical polarization methods were utilized to study the galvanic corrosion of steel coupled to brass. Polarization of a 70Cu-30Zn brass cathode controlled galvanic corrosion rate (...

Measuring the growth of oxide films on low carbon steel at 500°C by impedance spectroscopy

Abstract Oxide films, grown on low carbon steel in air at 500°C, were evaluated by concurrent room-temperature measurements of weight gain and impedance spectroscopy (IS). Weight-gain measurements displayed the expected parabolic kinetics due to growth of a relatively thick inner layer of magnetite (Fe 3 O 4 ). The Nyquist impedance spectra exhibited depressed semicircles, which were curve-fitted to obtain values of low-frequency film resistance, R , and capacitance, C . R was linear with oxidation time due to growth of a thin, porous, high-resistivity outer layer of hematite (Fe 2 O 3 ) over the underlying low-resistivity magnetite. IS shows promise for in situ non-destructive measurement of oxide scales on large low carbon steel surfaces during service by periodic measurements of oxide impedance. Further experimental measures are discussed to adapt impedance measurements to in situ determinations of oxide thickness.

Anodically enhanced diffusion in Cu/Ag thin film couples

Thin, 100-nm films of first silver and then copper were deposited consecutively onto pure single-crystal (111) silicon substrates by magneton sputter deposition. Controlled anodic current density was applied at room temperature to dissolve the outer copper film to varying depths approaching the copper/silver interface. Profiles of copper and silver concentration vs. depth below the anodically dissolved surfaces were subsequently obtained by argon ion sputtering and simultaneous Auger Electron Spectroscopy. Despite some intrinsic mixing during the profile analysis, there is clear evidence that diffusion of copper and silver into one another is enhanced by anodic currents at the outer copper surface. Preliminary interpretation leads the authors to believe that the effect is caused by surface formation of vacancies during anodic dissolution. The anodically generated vacancies can migrate as divacancies to the copper/silver interface where they enhance diffusion by the usual vacancy exchange mechanism.

The Advantages of Galvanostatic Polarization Resistance Measurements

Abstract A routine versatile galvanostatic procedure is described for measuring corrosion rate by polarization resistance. The galvanostatic procedure has been most useful and effective under transient conditons when corrosion rate and corrosion potential are changing with time or when relatively rapid corrosion potential fluctuations are present due to localized corrosion. At each step of the procedure, it is possible to monitor polarization to steady-state, a condition which has been found essential for accurate measurement of polarization resistance, especially at low corrosion rate. Comparisons are made with potentiodynamic scanning methods which have been favored in recent years.

Galvanic Interactions between Alloys and Minerals in Sulfuric Acid

Abstract Many semiconducting minerals have sufficient conductivity to permit electrochemical reactions on their surfaces. Consequently, galvanic interactions will occur when such minerals are coupled to metals or other conducting minerals. Accelerated galvanic corrosion of metals coupled to minerals is likely because most minerals exhibit potentials in solution that are noble to the corrosion potentials (Ecorr) of typical metal alloys. Anodic and cathodic polarization diagrams can be used to predict galvanic corrosion rates expected from any given galvanic couple in a particular corrosive electrolyte. Polarization diagrams were presented for numerous minerals and alloys in sulfuric acid (H2SO4). Examples demonstrated how the curves could be used to estimate the likelihood of galvanic corrosion and the reaction rates to be expected in metal-metal, metal-mineral, and mineral-mineral couples. The effects of relative cathode-to-anode surface area, application to initiation of pitting corrosion, and limitation...

Electrochemical Corrosion Behavior of Low-Carbon I-Beam Steels in a Simulated Yucca Mountain Repository Environment

Abstract The electrochemical corrosion behavior of low-carbon steel (CS) was examined in a simulated Yucca Mountain (YM) groundwater by varying the electrolyte concentration and temperature under a...