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A series of mechanical and electrochemical experiments were performed on samples of titanium aluminides, Ti3Al(α2) and iron aluminide (D03-Fe3Al). Electrochemical studies of these alloys in NaCl solution showed that Ti3Al is less susceptible to pitting corrosion than Fe3Al. Both materials were susceptible to stress corrosion cracking whenever the applied potential during stressing was greater than the breakdown potential. The mode of cracking was intergranular and most often multiple cracks were observed on the surface of tested samples. At applied potentials less than the breakdown potential susceptibility to localized corrosion decreased sharply and at the open circuit potential these alloys did not show any susceptibility. Hydrogen embrittlement (HE) was studied by cathodically charging samples with hydrogen. Ti3Al was very susceptible to HE and its tensile properties after hydrogen charging dropped sharply, while Fe3Al was less susceptible and no major changes in mechanical properties were observed. Oxidation rate of both materials were low up to 800 °C, but hot corrosion resistance in molten salt was extremely low. Severe localized corrosion was observed when samples were exposed to a molten sodium sulfate salt.

The recently developed I-P-Z model is modified in order to analyze the observed enhanced permeation of hydrogen that occurs in the presence of hydrogen sulfide during cathodic hydrogen charging of iron. The modification accounts for the fact that the energy of adsorption becomes coverage dependent at the higher coverages and affects the hydrogen evolution reaction (HER) in the presence of H2S. Charging experiments were performed on Ferrovac E-iron membranes 0.5 mm thick using a Devanathan-Stachurski cell in deaerated, pre-electrolyzed solutions made from 0.1 M HClO4 and 0.1 M NaClO4 with pH values of 1 and 2. The transfer coefficient, α, exchange current density, i0, thickness-dependent absorption-adsorption rate constant, k″, recombination rate constant, k3, surface hydrogen coverage, θH, and discharge rate constant, k1o, were obtained by application of the model to the experimental results. As a result, the role of H2S has been clarified. While θH is increased in the presence of H2S, the overpo...

A mechanistic model has been developed which for the first time considers the effect of hydrogen entry into a metal on the kinetics of the hydrogen evolution reaction (h.e.r.). The model enables computation of (i) the hydrogen surface coverage and surface concentration; (ii) the hydrogen adsorption, absorption, discharge and recombination rate constants; and (iii) the h.e.r. coverage‐dependent transfer coefficient, α, and the exchange current density , from a knowledge of the steady‐state hydrogen permeation current, cathodic charging current, hydrogen overvoltage, and hydrogen diffusivity. The model predicts a linear relationship between the permeation flux and the square root of the hydrogen recombination flux, and provides an analytical method to determine the cathodic potential range for operation of a coupled discharge‐recombination mechanism of the h.e.r. With modifications the model can treat permeation data for which (i) the mechanics of the discharge step involve a (proposed) selvedge reaction, and (ii) surface hydrogen coverages are relatively high as in the presence of poisons (e.g., or ). Some of the existing literature data for hydrogen permeation in iron and nickel in acid and alkaline solutions are successfully analyzed.