Electrochimica Acta, Vol.47, No.27, 4333-4338, 2002
Electrochemical noise analysis of cathodically polarised AISI 4140 steel. III. Influence of hydrogen absorption for stressed electrodes
In this third part of the study of the electrochemical noise generated by hydrogen evolution on cathodically-polarised AISI 4140 steel specimens in 0.5 M sulphuric acid, a tensile stress was applied to the specimens. The two components of the measured potential fluctuations DeltaV, namely ohmic-drop fluctuations DeltaR(e)I and faradaic potential fluctuations DeltaE, were analysed. After bubble size homogenisation, the effect of an applied stress was an increase in the level of the power spectral densities (PSD) Psi(V) and Psi(E) of the Delta V and DeltaE fluctuations, indicating a change in metal-hydrogen-interactions related to damages in the metal induced by the combined actions of stress and hydrogen embrittlement. In the meanwhile, the PSD Psi(ReI) of the ohmic-drop fluctuations did not exhibit any change, revealing that the departure rate and size of hydrogen bubbles were not modified by the internal damages in the specimen. The time evolution Of Psi(E) up to fracture could be explained by the enhancement of hydrogen penetration into the metal induced by the increase in the density of microdefects or crack advances inside the metal.
Keywords:electrochemical noise;hydrogen evolution;metal-hydrogen interactions;hydrogen embrittlement;potential fluctuations