Search results for "Pitting"
showing 10 items of 43 documents
Measurements of Positrons Lifetimes in Corroded Nickel
1999
It is over twenty years now that the nuclear method of conducting investigations into defects in the volume and on the surface of solids, based on positron annihilation phenomenon, has been developing on a quite intensive scale [1-3]. The present work is an attempt at adopting positron annihilation to investigations of the phenomenon of pitting corrosion in metals. Pitting occurs mainly in environments containing chlorides and affects metals and alloys covered with passivating oxide layers. Research carried out for many years by the use of various methods . has proved that pittings, which could — after some time — take sizes as large as the tenth of the millimeter order, are formed in the p…
Repassivation of the damage generated by cavitation on UNS N08031 in a LiBr solution by means of electrochemical techniques and Confocal Laser Scanni…
2010
Abstract The objective of this work is to study the influence of cavitation on the corrosion behaviour of Alloy 31, a highly-alloyed austenitic stainless steel (UNS N08031), in a LiBr heavy brine solution (992 g/L) at 25 °C. The presence of cavitation shifted the OCP value towards the active direction by 708 mVAg/AgCl, increased anodic current densities and passivation current density, ip, and reduced the pitting potential, Ep. Repassivation behaviour of Alloy 31 has been investigated by using potentiostatic tests at different potentials. The current density transient obtained after interrupting cavitation was used to obtain the repassivation index, n, provided by the slope of the log i(t) …
Investigation of pitting resistance of titanium based on a modified point defect model
2011
Abstract The pitting resistance of titanium was studied under potential control in solutions containing chloride ions. The results evidenced that Cl − concentration had an effect on the metastable pitting intensity, but no significant influence on the uniform corrosion. XPS characterization revealed that some Cl − ions were present in the outer hydroxide layer, but few in the inner oxide layer, indicating that the inner oxide layer was impervious to Cl − ions. A cation–anion-vacancy condensation mechanism was considered for pit initiation based on the point defect model (PDM). The experimental results analyzed by the charge integration technique were in agreement with the derived relations.
Evaluation of metastable pitting on titanium by charge integration of current transients
2010
Abstract The metastable pitting of titanium has been studied under potentiostatic control in solutions containing chloride ions. An approach based on the charge integration of current transients was proposed for a quantitative determination of metastable pitting. A pit density (dmpit) was defined as the number of metastable pits per unit area per unit time (cm−2 h−1) with a typical size, instead of a size distribution. The calculated dmpit of titanium at 0.5 VSCE in 0.6 M NaCl was about 1.0 × 103 cm−2 h−1 with a typical radius of 0.12 μm. An exponential potential dependence of dmpit was obtained through the integration approach.
Influence of an elastic stress on the conductivity of passive films
2001
Abstract The electrochemical impedance was measured over a large range of frequency and under straining condition in sodium chloride solution. The Mott-Schottky analysis, performed at high frequency, appears as very useful method to study the effect of an elastic stress on the capacitance values. The results obtained indicate that the semi-conductive properties of passive films formed on a type 316 L stainless steel (SS) are not markedly modified by an elastic stress when applied after ageing. In contrast, passive films formed in the presence of elastic stress have a higher donor and acceptor concentration than those formed in a stress-free state, suggesting that the passive film conductivi…
Passive Behavior and Passivity Breakdown of AISI 304 in LiBr Solutions through Scanning Electrochemical Microscopy
2014
The passive behavior and passivity breakdown of AISI 304 stainless steel in LiBr solutions has been investigated by means of scanning electrochemical microscopy (SECM). The sample generation - tip collection (SG-TC) mode was used to operate the SECM and the tip potential was biased to detect the electroactive species. The evolution of the current at the ultramicroelectrode tip with the applied potential within the passive range was followed at different LiBr concentrations. Results show that the absolute value of the current at the tip increases with the applied potential. Additionally, SECM was also used to detect stable pits formed on the stainless steel surface in a 0.2 M LiBr solution. …
Influence of the Chemical Dissolution of MnS Inclusions on the Electrochemical Behavior of Stainless Steels
2005
Immersion of stainless steel containing a well-controlled density of MnS inclusions in 1 M NaCI, pH 3 leads to the chemical dissolution of these heterogeneities. This process was studied using in situ atomic force microscopy and the dissolution rate of MnS inclusions was estimated between 0.01 and 0.19 μm 3 /min. The effects of MnS dissolution on the chemical composition and the local electrochemical behavior of the specimen surface were investigated using secondary ion mass spectroscopy, X-ray photoemission spectroscopy, and the electrochemical microcell technique. It was shown that stable CrS and unstable FeSO 4 were formed. The size of the areas around MnS inclusions affected by the pres…
Influence of the microstructure on the corrosion behaviour of low-carbon martensitic stainless steel after tempering treatment
2014
Abstract The microstructure of grade X4CrNiMo16.5.1 stainless steel was studied at different scales. The chemical composition of the native passive film formed on the different phases was then determined at the microscale. The degree of homogeneity of the native passive film is discussed. Subsequently, the susceptibility to pitting corrosion of X4CrNiMo16.5.1 was quantified using the electrochemical microcell technique. The nature of precursor sites and the morphology of pits were investigated by combining scanning electron microscopy with Electron BackScatter Diffraction and potentiostatic pulse tests. The role of the microstructure and the cold-worked layer generated by polishing in pitti…
Engineering failure analysis of corroded R.C. beams in flexure and shear
2018
Abstract In the present paper, a simple model to reproduce the load-deflection response of corroded beams failing in flexure and shear is presented and discussed. Effects of diffused and pitting corrosion on steel bars, compressive concrete strength degradation and concrete bond strength degradation due to rust formation are included in the model. Engineering approach based on limit state theory was here adopted to predict the peak and the residual flexural and shear strength of corroded beams with corresponding deflections and ductility estimation. Calculation of deflection at cracking taking into account of rust formation and deflection at yielding and the ultimate state taking into accou…
Influence of the chemical dissolution of MnS inclusions on the composition of passive films and the local electrochemical behaviour of stainless stee…
2006
Abstract Immersion of stainless steel containing MnS inclusions in aqueous electrolytes leads to the chemical dissolution of these heterogeneities. Chemical dissolution of MnS inclusions in 1M NaCl, pH=3 was studied using in-situ AFM and the dissolution rate of MnS was estimated between 0.04 and 0.19 μm 3 /min. The local electrochemical measurements reveal that the chemical dissolution of MnS inclusions promotes pitting corrosion. Similary, chemical dissolution of MnS inclusions in IM NaClO 4 , pH=3 solution modified the surface close to the inclusions by the presence of FeSO 4 in the passive film.