D. Gorse

Synergy effect of LBE and hydrogenated helium on resistance to LME of T91 steel grade

Abstract The aim of this paper is to determine the influence of the environment on the resistance to LME of the T91 steel/LBE system. First, we recall that a few hours of exposure to LBE under flowing hydrogenated helium (He–4%H 2 ) is sufficient to modify the corrosion resistance and wettability of T91 steel, once the temperature attains 350 °C. This result is consistent with a degradation of the protectiveness of the surface oxide film with increasing temperature from 150 to 350 °C, in present experimental conditions. Then, the tensile properties of T91 steel are studied as function of the temperature and cover gas. A reduction in strength and ductility of T91 steel is found, passing through a maximum at the temperature of 350 °C under flowing He–4%H 2 , and suggesting a synergy effect of LBE and hydrogenated helium.

Comprehensive Dissolution Current Noise Analysis during Stress Corrosion Cracking of Cu3Au Alloys

Potentiostatic electrochemical noise measurements are performed on Cu{sub 3}Au polycrystals over the whole duration of slow strain rate tensile testes up to brittle cracking in acidic sulfate medium. According to previous works, three different potential testing conditions are chosen, which lead to a more or less enhanced embrittlement. At first glance, one observes successively silent and active electrochemical zones over the whole duration of the mechanical test. Qualitative signal analysis using deterministic chaos theories reveals that (i) the electrochemical behavior of the strained specimen is purely deterministic, (ii) the local maximum Lyapunov exponent, {lambda}{sub 1}, is sensitive to corrosion-deformation interactions, and (iii) there is a clear tendency of {lambda}{sub 1} to decrease well before entering in the crack propagation regime, regardless of the electrochemical conditions used.

Stress Corrosion Cracking Behavior of α-Brass as a Function of the Oxide Transport Properties in NaNO2 Solutions

In this paper, we relate the transport properties of the anodic oxide films formed on α-brass in NaNO 2 solutions to the mechanical response of the alloy during slow strain rate tensile tests. A range of electrolyte concentrations were investigated, from 5 X 10 -4 M (pH 7.1) to 8.4 M (pH 8.8). Surface analysis [X-ray photoelectron spectroscopy, Auger electron spectroscopy (AES), and AES depth profiling] techniques were used to investigate the films composition. We begin by defining an electrochemical and mechanical criterion of crack initiation. Then three concentration regimes are revealed, for which a net correlation can be established between the oxide film permeability to metal cations and the susceptibility to stress corrosion cracking (SCC): (i) in the dilute regime, the passive film on α-brass is highly permeable while crack initiation requires high mechanical loading; (ii) in the intermediate regime, both the protective character of the oxide film and the susceptibility to SCC are maximum; and (iii) in the concentrated regime, on the contrary, both the film permeability and the extension of the plastic domain are increasing with NaNO 2 concentration.