Influence of an elastic stress on the conductivity of passive films

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…

Droplet cell investigation of intergranular corrosion on AA2024

An original method combining a droplet cell with direct optical interrogation of the reverse side of a 50μm thick foil AA2024 has been tested to evaluate the possible analysis of the current during intergranular corrosion tests. The foil microstructure and the selected orientation were suitable for recording the current generated during the propagation in volume of a well-defined grain boundary trace. Even if it is impossible to reach a charge and mass balance from these preliminary attempts, it was demonstrated that it is possible, despite hydrogen evolution, to record a current transient resulting from the full penetration of an intergranular path. Keywords: Intergranular corrosion, Alumi…

Study of the Chemical Conversion of Aluminum Alloys by Coupling CFDE and EQCM

The ability of the channel flow double electrode (CFDE) technique and electrochemical quartz crystal microbalance (EQCM) for studying in situ chromate phosphate conversion coating on 5182 aluminum alloys was explored. It was first demonstrated that aqueous Cr(VI) can be analyzed quantitatively with the CFDE technique by reduction into Cr(III) on a graphite electrode. Samples used for EQCM were quartz plated by physical vapor deposition using a 5182 alloy target, allowing thin layers of aluminum alloys with a similar chemical composition to be obtained. EQCM was adapted in order to account for the hydrodynamic conditions in an industrial process, by placing the quartz in a flow cell. In orde…

Renforcement de la résistance à la corrosion localisée de l’acier inoxydable 304L grâce au traitement de surface par laser impulsionnel

L’acier inoxydable 304L est utilise dans de nombreux domaines. Cependant, il peut, dans certaines conditions, etre sensible a la corrosion par piquration. Dans cette etude, nous nous sommes interesses aux potentialites du traitement de fusion superficielle par laser nanopulse pour l’amelioration de la resistance a la corrosion de cet acier. Ce traitement consiste a focaliser un faisceau laser sur la surface du materiau, provoquant sa fusion quasi instantanee sur quelques microns, immediatement suivie d’un refroidissement ultra-rapide allant jusqu’a 1011 K/s. Les parametres laser impliquent des modifications des proprietes physico-chimiques. Nous avons notamment etudie l’influence du recouvr…

Laser induced decohesion of coatings: probing by laser ultrasonics.

The aim of the present study is to investigate a conventional laser-ultrasonics technique for the determination of intrinsic properties of oxide coatings and their adhesion strength on a metallic substrate. The good agreement between experiments and computations in an epicenter configuration allows determining the longitudinal wave velocity as well as the Young's modulus of the oxide coatings versus the porosity. For a critical value of the laser energy, a breakdown at the coating-substrate interface is generated by the laser irradiation. The critical tensile stress field developed at the coating/substrate interface, which leads to the interfacial fracture, can be easily calculated. The val…

Investigation of self-healing mechanism on galvanized steels cut edges by coupling SVET and numerical modeling

Local cathodic inhibition has been observed on the cut-edge of galvanized steel immersed in 0.03 M NaCl solution using the scanning vibrating electrode technique. The current distribution results indicate that cathodic inhibition occurs in a limited spatial zone located between the cathodic sites on the steel and the anodic sites on the exposed zinc surface. The experimental current distributions are compared with the results of numerical simulations that show the specific diagnostic features for the detection of cathodic inhibition from scanning vibrating electrode technique (SVET) data so as to distinguish the zero current regions from experimental artifacts due to the lateral resolution …

Numerical modelling of the galvanic coupling in aluminium alloys: A discussion on the application of local probe techniques

Abstract A discussion is proposed on the determination of the input values and the experimental validation of finite element modelling of the galvanic coupling in aluminium alloys by local probe techniques such as the Scanning Vibrating Electrode Technique (SVET) and the microcapillary electrochemical cell (microcell). Polarization curves obtained by the microcell were introduced as input conditions in the model based on Laplace or Nernst–Planck equation. SVET measurements were performed to determine the coupling current distribution on an Al/Al4%Cu bimetallic system. Agreement was found between simulated and experimental current distributions depending on the input conditions and the solve…

Application of total internal reflexion fluorescence microscopy for studying pH changes in an occluded electrochemical cell: Development of a waveguide sensor

A device for pH mapping derived from optical sensors similar to total internal reflection fluorescence microscopy (TIRFM) has been developed for future possible applications in the field of localized corrosion. The sensing principle is the increase of the fluorescent yield of the fluorescein with the pH of the medium. The basic principle of this sensor is based on the excitation of a fluorescent silica polymer film of nanometre dimensions, deposited by sol–gel method on a waveguiding layer. The total internal reflexion conditions creates an evanescent wave which interacts with the molecules trapped in the silica layer. A conventional microscope located above the sample collects the fluoresc…

Electrochemistry for Mechanically-assisted Corrosion

Abstract: This chapter will not discuss the basics of electrochemistry; these aspects have been largely developed in the previous corrosion thematic school on stress corrosion cracking (SCC).

High spatial resolution strain measurements at the surface of duplex stainless steels

International audience; The determination of local strain fields at the surface of materials is of major importance for understanding their reactivity. In the present paper, lithography is used to fabricate grid points at the microscale and to map strain gradients within grains and between grains. This method was applied to duplex stainless steels which exhibit heterogeneous strain distributions under straining conditions. The influence of various parameters (the specimen microstructure, the density of slip bands, the number of systems activated and the grid geometry) on the strain value was discussed.

The anodic and cathodic dissolution of Al and Al–Cu–Mg alloy

Abstract Atomic emission spectroelectrochemistry (AESEC) was used to monitor the release of Al from 99.99% aluminum (1199 alloy) and Al, Mg, and Cu from 2024 Al alloy in 30 g/l NaCl electrolyte as a function of pH. The cathodic dissolution of Al was demonstrated and attributed to an increase in the pH at the interface due to the water reduction reaction. The dissolution of Mg was also observed but was a more complex function of current probably depending on the interfacial pH and the Al dissolution rate. The detachment of copper-rich particles was observed as very rapid spectroscopic emission transients (peak width

Use of the electrochemical microcell technique and the SVET for monitoring pitting corrosion at MnS inclusions

The purpose of this paper is to report on use of the electrochemical microcell technique and the scanning vibrating electrode technique for monitoring pitting corrosion on the same stainless steel microstructure. First, the electrochemical behaviour of sites containing a single inclusion was investigated in order to the determine both the successive steps occurring during the inclusions activation and some key-parameters such as the onset potential for MnS dissolution and the pitting potential. Then, the local current distribution around a pitting site was monitored at open circuit potential in order to locate anodic and cathodic regions and to obtain informations on the galvanic coupling b…

A pulsed laser technique for an evaluation of the spall resistance of sputtered oxide films: diagnostic by interferometric probing

Abstract A pulsed laser technique, based on conventional laser acoustics testing, has been developed to define the spall resistance of sputtered oxide films on a metallic target. Direct irradiation of the coated side of the sample generates an acoustic source at the inner film–metal interface. A model of the laser-induced epicentral displacements at the opposite side that takes into account the confining effect of the coating has been proposed to evaluate the critical laser irradiance corresponding to progressive damages at the inner film–metal interface, i.e. interface delamination, film spallation and film expulsion, respectively. The behavior of Al 2 O 3 and ZrO 2 films deposited by PVD …

Surface acceleration during dry laser cleaning of silicon

We report on measurements of the surface acceleration for the application of dry laser cleaning. For that purpose, industrial silicon samples were irradiated by a frequency-doubled Q-switched Nd:YAG laser. The surface displacement was measured by a heterodyne interferometer and recorded by a digital storage oscilloscope. Several hundreds of shots were averaged to give smooth displacement curves which could be derived numerically. The experiments show that the highest accelerations, which are thought to be responsible for the cleaning, occur on the time scale of the laser pulse. Simple theoretical models are in good agreement with the experimental data. The maximal displacement depends only …

Effect of the surrounding aeration on microcapillary electrochemical cell experiments

In the microelectrochemical capillary cell technique a silicone rubber gasket is used to avoid any electrolyte leakage between the pulled glass capillary and the working electrode (the metallic tested material). In this study, it is demonstrated that the oxygen reduction reaction (ORR) is strongly affected by the use of the silicone rubber. Experiments under a surrounding argon gas shielding of the pulled capillary in contact with the metallic surface have been performed showing a large effect on the ORR. Considering the high permeation rate of oxygen through silicone, the decrease of the reaction rate observed experimentally was validated by FEM modelling assuming that the air/silicone/wat…

Surface modifications induced by nanosecond pulsed Nd:YAG laser irradiation of metallic substrates

International audience; Substrate surface preparation is a key step in coating deposition process. In recent years, pulsed laser cleaning has emerged as a possible technique to challenge the traditional preparation methods (based on degreasing and eventually grit-blasting). The laser operated at short-pulse mode offers high cleaning efficiency and therefore has been largely used. In a specific process named PROTAL®, a nanosecond pulsed laser is introduced to prepare the surface simultaneously to thermal spraying, with the purpose of eliminating the contaminants and generating favorite surface conditions for coating deposition. This study aims at clarifying some fundamental aspects of nanose…

Predictive Model for Cut-Edge Corrosion of Galvanized Steels

A numerical model for the electrochemical behavior of cut-edge of galvanized steels is proposed. Some experimental data of current densities above cut-edge immersed in a 0.03M NaCl solution have been measured, using a scanning vibrating electrode technique, and compared with some simulated ones. A good fit has been obtained. The model geometry has been modified by decreasing the electrolyte thickness in order to tend towards an atmospheric corrosion case; such situation that is not easily accessible by electrochemical studies. Three regions can be distinguished according to the efficiency of the galvanic coupling to protect steel.

Study of the mechanical effects on passivity breakdown by local probe techniques

This paper aims at demonstrating that a relationship exists between surface stress and pitting corrosion. The surface stress field generated by polishing was first calculated using a thermo-mechanical model and a finite element code. Pitting corrosion tests performed at the microscale along the austenite/ferrite interface using the electrochemical microcell technique were then analyzed considering the microstructure and the residual surface stress field. Mechano-chemical criteria are proposed leading to an enhancement of pitting corrosion of duplex steels.

Impedance characterization of the electrochemical environment under a polymer film artificially delaminated

International audience; Knowledge of the electrical conductivity of the zone under a delaminated paint film is one necessary input parameter for the simulation of electrochemically driven underpaint corrosion. In this work, a microelectrode array system has been developed, tested, and applied to measure the spatial distribution of resistivity in the delaminated zone along the metal/polymer interface. The experimental device consists of a linear array of six 100 m diameter stainless steel microelectrodes (100 m in diameter) embedded in a steel substrate. A polymer coatingwas applied and an artificial "delaminated zone"was created using the laser-induced decohesion technique. The electrochemi…

Corrosion in amine units for acid gas treatment : a laboratory study

International audience; Corrosion represents one of the most important operational issues in amine units used for acid gas treatment. Considerable experience is available in the literature both on laboratory and in the field. Based on this experience, proven mitigation strategies are available, using corrosion inhibitors or corrosion resistant alloys at selected locations in the plant. However, the technical causes of the corrosivity of amine solvents are still not well understood. Furthermore, recent field experience showing severe corrosion in sweet units pointed out the difficulty to transpose design solutions from sour to sweet gas. There is obviously a need for more precise data on the…

Inhibition Probing on a Cut-Edge Electrode Machined from a Primer-Coated 2024-T3 Alloy

Conventional corrosion protection of 2024-T3 alloys (AA2024T3) in aeronautic structures combines conversion coating with chromate-inhibited primer protected by a top-coat. In some cases this protection can break down after mechanical damage to the paint systems inducing a risk of localized corrosion if the release of inhibitors trapped in the primer does not reach a critical level. There is a need for developing computational models combining the inhibitor release and transport within and from the coating system andthecorrosioninhibitionprocess,toassistinthedesignofnewmultifunctionalcoatingsystems.Theinfluenceonthecorrosioninhibition of various parameters such inhibitor release rate, defect…

Influence of the dissolution of MnS inclusions under free corrosion and potentiostatic conditions on the composition of passive films and the electrochemical behaviour of stainless steels

Abstract The influence of the dissolution of MnS inclusions at the OCP value and 400 mV versus SCE on the chemical composition of passive films and the electrochemical behaviour of resulfurized austenitic stainless steel was studied in 1 M NaClO 4 , pH 3, solution using SIMS, XPS, electrochemical impedance spectroscopy and the electrochemical microcell technique. The electrochemical dissolution (at 400 mV versus SCE) of inclusions occurred uniformly along the interface and this process was almost complete after 25 min immersion. A small amount of sulfur was detected on the matrix that exhibited a wide passive range. By contrast, the dissolution process under free corrosion was not uniform a…

Progres recents des etudes de corrosion sous contrainte

Effect of microstructure and chemical composition on localized corrosion resistance of a AISI 304L stainless steel after nanopulsed-laser surface melting

Abstract Changes induced in the surface properties of AISI 304L stainless steel when it is treated with a nanopulsed ytterbium-doped fiber laser were investigated to determine the microscale distribution of its physico-chemical properties. A Gaussian energy distribution was created with a radius of 71 μm (1/e2) at the focal point. Local investigations were carried out using transmission electron microscopy to consider the effect of overlapping individual laser impacts. The results obtained reveal that laser surface melting leads to changes in the crystallographic structure of the steel through the formation of a δ-ferritic phase. It also results in the creation of an oxide layer that increa…

Protective mechanisms occurring on zinc coated steel cut-edges in immersion conditions

Abstract Electrochemical processes occurring on the cut-edge of a galvanized steel immersed in NaCl solutions were studied using numerical simulations, and in situ current and pH profiles measured over the cut-edge. These results clearly demonstrate that only the steel surface remote from the zinc coating is cathodically active, oxygen reduction being strongly inhibited in the vicinity of zinc. This trend was confirmed by local polarization curves recorded on these distinct areas. Ex-situ AES and SEM analysis and cathodic polarization curves in solutions containing Zn 2+ ions led to conclude that this cathodic inhibition was related to the fast nucleation of a dense Zn(OH) 2 film on the ste…

Enhancement of pulsed laser removal of metal oxides by electrochemical control

Pulsed laser irradiation of oxidized metallic surfaces in an electrolytic cell under proper voltage conditions is demonstrated to be a promising new approach for effective removal of oxide films. Systematic measurements on simulated corrosion-product films by optical reflectance profile and energy dispersive X-ray spectroscopy are used to study the physical mechanisms of this novel phenomenon, the physical conditions for its observation and its possible generality. It was observed that the utilization of a basic electrolyte solution and the imposition of a certain cathodic potential prior to laser irradiation is an essential requirement for a high removal efficiency. This new technique has …

In situ diagnostics and control of laser-induced removal of iron oxide layers

The mechanism of laser-induced removal of thermally grown iron oxide layers on pure iron has been investigated by means of in situ reflectivity measurements. The experiments were carried out by irradiating the sample with λ=584 nm, τ=6 ns (FWHM) laser pulses in a buffer borate solution after a cathodic polarisation of - 1.5 V/SCE had been applied during 40 min. The removal efficiency has been studied as a function of the number of laser pulses, for several fluence values and for a few time delays after switching off the cathodic polarisation. The results demonstrate that reflectivity measurements are a suitable non-invasive in situ diagnostics tool for the assessment of the efficiency of ox…

Influence of the Chemical Dissolution of MnS Inclusions on the Electrochemical Behavior of Stainless Steels

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…

On the topographic and energetic surface modifications induced by laser treatment of metallic substrates before plasma spraying

Abstract Laser surface cleaning has been proven as a very suitable technique for the substitution of some surface preparation steps, such as wet cleaning and grit blasting. The mechanisms involved in short pulsed laser ablation include the absorption of the laser light and conversion into heat via collisional processes. Ejection of matter is achieved either by direct vaporization or hydrodynamical sputtering. This article aims at clarifying the laser–matter interaction mechanisms and effects on metallic materials for different surfaces initial roughness and laser beam energy densities. Both topographic and energetic modifications are investigated by SEM observations, roughness characterizat…

Surface modifications induced by pulsed-laser texturing—Influence of laser impact on the surface properties

Abstract Laser cleaning technology provides a safe, environmentally friendly and very cost effective way to improve cleaning and surface preparation of metallic materials. Compared with efficient cleaning processes, it can avoid the disadvantages of ductile materials prepared by conventional technologies (cracks induced by sand-blasting for example) and treat only some selected areas (due to the optical fibers). By this way, laser technology could have several advantages and expand the range of thermal spraying. Moreover, new generations of lasers (fiber laser, disc laser) allow the development of new methods. Besides a significant bulk reduction, no maintenance, low operating cost, laser f…

Analogy between the effects of a mechanical and chemical perturbation on the conductivity of passive films

Abstract In order to study the passivity breakdown of a type 316L stainless steel, the electrochemical impedance and surface stresses were measured under straining conditions. The Mott–Schottky analysis, performed at high frequency, appears as very useful method to study, below the apparent yield strength, the effects of a mechanical stress on the capacitance values. The results obtained in sodium chloride media indicate that the semiconducting properties of passive films formed in a tensile stress field reflect a higher vacancies concentration than those formed in a stress-free state, suggesting that the passive film conductivity is increased. It was also shown that the Mott–Schottky plots…

Real-Time Monitoring of Intergranular Corrosion Damage on AA2024

The total porosity induced by the intergranular corrosion was selected as a monitoring parameter to follow in real-time the defect propagation of AA2024. The pertinence of eddy current (EC) probing has been tested on very thin foils of AA2024 (30 μm in thickness) in immersion conditions under potentiostatic control and in atmospheric conditions simulated by controlled salt spray experiments. Combining this nondestructive evaluation technique with a direct optical interrogation of the backside of the test specimen (derived from the foil penetration technique) allows one to discuss the contribution of both the dissolution in the depth and along the grain boundaries to the total porosity. In i…

Simultaneous laser generation and laser ultrasonic detection of the mechanical breakdown of a coating–substrate interface

Abstract The present study deals with information that could be obtained by real-time contactless monitoring of the normal displacement, due to the propagation of the longitudinal waves generated by nanosecond pulsed laser irradiation, through a transparent and porous ceramic coating deposited on a metallic substrate. These displacements were recorded in real-time at the rear surface of the specimens using a laser heterodyne interferometer and were correlated with the different steps of laser/material interaction (thermoelastic interactions, fracture of the coating–substrate interface and coating expulsion). An analytical model was developed to establish a relation between the longitudinal …

Laser-ultrasonics: a non-contact method to link the acoustic attenuation to metal damping properties up to the melting point

The objective of this work is to describe the viscoelastic behavior of metals up to their melting temperature by measuring the velocity and the attenuation of ultrasonics waves. For that purpose, a technique called laser-ultrasonics has been optimized for the high temperature domain and the solid to liquid transition. This paper is especially applied to the viscoelastic characterization of tin, from room temperature up to the melting point.

Modeling bimetallic corrosion under thin electrolyte films

A finite element model (FEM) was developed to calculate the potential distribution in the electrolyte in the case of bimetallic corrosion between iron and zinc electrodes, taking into account mass transport of oxygen in the solution. This model was first compared with experimental results obtained by scanning vibrating electrode technique (SVET) on a galvanized steel cut-edge in immersion conditions in a 0.03 M NaCl electrolyte. A good agreement was obtained between the calculated and experimental current densities. The model predicted the evolution of the galvanic coupling as function of the electrolyte thickness and for various iron–zinc surface area ratios. Different coupling regimes wer…

Pulsed laser cleaning of oxidized metallic surfaces in electrochemically controlled liquid confinement

Pulsed laser cleaning of oxidized metallic surfaces is studied. To our knowledge, for the first time, it has been demonstrated that the application of pulsed laser irradiation in a liquid confinement at controlled electrochemical potential enhances the oxide film removal from metal surfaces. Systematic studies on simulated corrosion product films using optical reflectance profile, energy dispersive X-ray spectroscopy, and piezoelectric transducer measurements, have revealed that efficient oxide film removal by laser irradiation is achieved if a basic electrolyte solution is used and a cathodic potential is imposed. The advantages of this novel technique against laser irradiation in air are …

Cut-edge corrosion of a Zn–55Al-coated steel: A comparison between sulphate and chloride solutions

Abstract Ex situ observations and in situ measurements of current and pH distributions over cut-edge coated steels revealed that Zn–55Al coatings are sacrificial only in chloride solutions, because of an activation of both Zn- and Al-rich phases present in the coating. In sulphate solutions, an efficient cathodic protection occurs only for short times of immersion, because only Zn-rich phases are active in this medium. The low solubility and strong acidification induced by Al(OH)SO4 allows only short distance cathodic protection, but cannot prevent red rust precipitation on the steel surface.

Effect of Aeration on the Microelectrochemical Characterization of Al[sub 2]Cu Intermetallic Phases

Local probing of the galvanic coupling between micrometer-sized Al 2 Cu phases and the surrounding aluminum-based matrix of a specially heat-treated 2011 alloy is investigated using a microcapillary electrochemical cell. The aging of an isolated Al 2 Cu particle, i.e., selective dissolution of aluminum, is controlled by the aeration condition at the tip of the capillary due to the nature of the silicon membrane used as a gasket. The local electrochemical behavior of an isolated particle after aging confirms the mass transport control of the oxygen reduction on the galvanic coupling of the particle with the surrounding matrix.

A lap joint simulant laboratory test method of aluminium alloys

A lap joint simulant cavity (LJSC) with a gap thickness of 200 μm has been developed to test corrosion of assembled coated aluminium alloys. The LJSC was instrumented with electrodes allowing simultaneous pH and potential measurements in 0.5 M NaCl solution. Assuming the outer part of the LJSC is electrochemically inactive (painted sheet) it was confirmed that in free corroding conditions the pH inside the LJSC tends more towards alkalinisation. On the opposite, if the outer part of the LJSC is electrochemically active (unpainted sheet) the pH inside the LJSC tends towards an acidic value.

Corrosion in alkanolamine used for acid gas removal: From natural gas processing to CO2 capture

The aim of this paper is to review some of the parameters influencing the corrosivity of alkanolamine solvents used for natural gas purification or for CO2 capture. In the light of literature data and of new experimental results, the influences of temperature and of acid gas loading are discussed. These two parameters appear to have a strong impact on corrosion rates of carbon steel, with extrapolated corrosion rates of several tens of mm/year for the highest temperature and acid gas loading condition.

Recent advances in local probe techniques in corrosion research – Analysis of the role of stress on pitting sensitivity

Local probe techniques have been largely applied to predict the spatial distribution of the electrochemical reactions and to quantify the corrosion rate. These local probe techniques are now being developed to capture the temporal information, in-situ and in real-time. Nevertheless only few works have been devoted to investigate with these local probes the role of stress on pitting sensitivity on passive materials. In this paper, a part of the most recent studies based on combination of local electrochemical measurements with finite element mapping of surface stress gradients are reported illustrating the role of inclusions under straining and the mechanical effect of surface preparation on…

Quantification of Plasma Sprayed Coating Adhesion Using Pulsed Laser Induced Decohesion Technique

Abstract The aim of the present study is to compare a laser ultrasonic technique with a conventional indentation test for the determination of intrinsic properties and the adhesion of alumina coatings, of different thicknesses (30–350 µm), deposited on stainless steel substrates by atmospheric plasma spraying (APS). For this purpose, a pulsed Nd:YAG laser is used to irradiate the coated specimens, and the ultrasonic waves generated by the laser are recorded at the epicenter using a laser interferometer. In the thermoelastic regime, the good agreement between the experiment and computation allows determination of the longitudinal wave velocity as well as the Young's modulus of the oxide coat…

Simulation of pH-controlled dissolution of aluminium based on a modified Scanning Electrochemical Microscope experiment to mimic localized trenching on aluminium alloys

Abstract Some constituent intermetallic (IMPs) particles at the surface of aluminium alloys are considered as preferential sites for the initiation of structural corrosion resulting in localized trenching around the particles and the surrounding Al matrix. In this work, a modified scanning electrochemical microscope (SECM) experiment was used to induce such phenomena via a local alcalinisation on 200 nm thick aluminium coatings promoting their local dissolution in an aerated 0.1 M NaCl electrolyte. The local alcalinisation was induced by the oxygen reduction reaction on the tip of a SECM which mimics the surface of an isolated IMP. From a phenomenological point of view, reproducible cylindr…

Laser cleaning of oxide iron layer : efficiency enhancement due to electrochemical induced absorptivity change

Laser cleaning experiments exhibited a higher cleaning efficiency of the laser cleaning upon application of electrochemical potential on an oxidised iron surface. The objective of this study is to clarify the role of such an electrochemical control on cleaning efficiency. Therefore a study by optical spectrometry at normal incidence in the relevant conditions was performed. From these measurements the optical parameters n and k were deduced. While n is mainly not affected, k changes for a factor of 10 upon application of an electrochemical potential. These results explain the differences in laser cleaning efficiency due to the modified absorption length.

Reliability of numerical models for simulating galvanic corrosion processes

International audience; Maturity of numerical simulation represents an important issue in the development of predictive models of galvanic corrosion. As widely used in electrochemical engineering, a coupled electrochemical-transport-reaction (CETR) model is recommended to simulate the current distribution above a galvanic corrosion cell made of the cut-edge of a galvanized steel sheet. Nevertheless, simulating current density distributions obtained experimentally by scanning vibrating electrode technique (SVET) above such a galvanic cell appears to be more accurate using an electrostatic model considering a homogeneous conductivity. In this case, the absence of concentration gradients next …

The use of local electrochemical probes and surface analysis methods to study the electrochemical behaviour and pitting corrosion of stainless steels

Abstract In this paper, the electrochemical microcell technique is combined with ex situ (SIMS and XPS) and in situ (SVET) techniques to study the electrochemical behaviour and pitting corrosion of inclusion-contaning stainless steels. Dissolution of metallurgical heterogeneities, depassivation and pitting mechanisms are first discussed in 1 M NaClO4, pH 3, and 1 M NaCl, pH 3, by considering the chemical composition and morphology of inclusions. The influence of the chemical composition of passive films on the electrochemical reactions and the microgalvanic coupling processes occurring at the corrosion potential is also investigated on the same specimen microstructure.

Study of localized pulsed laser depassivation by interferometric probe

Optical interferometry has been implemented as a novel approach to monitor sensitively the localized pulsed laser depassivation of iron or stainless steel samples. This new method, complementing the previous transient current measurements and channel flow double-electrode, is based on the time-resolved measurement of the rear surface displacement of the test sample induced by the laser generated ultrasonic wave. The removal of any material, such as the passive film, from the irradiated surface results in an enhancement of the longitudinal component of the laser generated ultrasonic wave, which is manifested in a change of the displacement characteristics of the rear surface of the test samp…

In situ investigation of sacrificial behaviour of hot dipped AlSi coating in sulphate and chloride solutions

Abstract The electrochemical behaviour of the cut-edge of hot-dipped aluminium–silicon-based alloy coated steel is studied in immersed conditions in sulphate and in chloride media. Preliminary studies performed on steel-pure Al bi-electrode demonstrate that a significant galvanic current can develop at short times (t

Evaluation of viscoelastic constants of metallic materials by laser-ultrasonics at elevating temperature

The main objective of this study is the determination of elastic moduli and viscosity coefficients of metals at elevating temperature up to melting point. More specifically, it involves the analysis of the propagation of acoustic waves generated and detected simultaneously by laser-ultrasonic for the measurement of longitudinal and shear velocities. This preliminary work primarily concerns Tin (Sn) metal known for its low melting point and attenuation coefficient.

Laser Ultrasonic Testing for Estimation of Adhesion of Al2O3Plasma Sprayed Coatings

Abstract The aim of the present study was to investigate the possibility of using a laser ultrasonic technique for the estimation of the adhesion of ceramic coatings, deposited onto metallic substrates by thermal spraying techniques. For this purpose, a pulsed Nd : YAG laser (λ = 1064 nm, 14 ns) was used to irradiate Al2O3 coatings, of different thickness (30–350 µm), deposited onto stainless steel substrates by atmospheric plasma spraying. The laser generated ultrasonic waves were in situ recorded at the epicentre using a laser heterodyne interferometer. The acoustic waveforms were correlated with the interaction between the pulsed laser radiation and the coated metal, taking into account …

Influence of the Chemical Composition and Electronic Structure of Passive Films Grown on 316L SS on Their Transient Electrochemical Behavior

Modifications of the passive film formed on 316L stainless steel (SS) in acidic media were performed under dc or ac polarization. The effects of these ageing treatments on the chemical composition and the electronic structure of the passive film were studied. Chemical analysis with angle resolved X-ray photoelectron spectroscopy revealed that ageing induces a net enrichment in chromium oxide in the inner part of the passive film and an increase of the thickness of the inner oxide. Semiconducting behavior of the passive films was revealed by a Mott-Schottky analysis. The passive film was considered as a dielectric with different trapping levels lying in the bandgap. The observed n- or p-type…

Nanosecond laser surface modification of AISI 304L stainless steel: Influence the beam overlap on pitting corrosion resistance

Abstract Surface modifications of AISI 304L stainless steel by laser surface melting (LSM) were investigated using a nanosecond pulsed laser-fibre doped by ytterbium at different overlaps. The objective was to study the change in the corrosion properties induced by the treatment of the outer-surface of the stainless steel without modification of the bulk material. Different analytical techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), and glow discharge optical emission spectrometry (GDOES) were used to characterize the laser-melted surface. The corrosion resistance was evaluated in a chloride solution at room temperature by electrochemical tests. The results sh…

Influence of magnesium content on the corrosion resistance of the cut-edges of Zn–Mg-coated steel

Abstract The ability of Zn–Mg coatings (with magnesium content between 5.8 and 15.5 wt.%) to protect steel sheets has been evaluated with local electrochemical techniques (scanning vibrating electrode technique, microcapillary electrochemical cell) and rotating disk electrode, and compared with the corrosion protection afforded by a pure zinc coating. From immersion tests of coated steel cut-edges, it is observed that alloying zinc with magnesium leads to a decrease of the galvanic current between the coating and the steel surface, and to an improvement of the steel corrosion resistance after a drying period, due to the presence of magnesium in the corrosion products.

SVET, AFM and AES study of pitting corrosion initiated on MnS inclusions by microinjection

As pitting is a random phenomenon, it is difficult to predict where a pit will appear on the surface and consequently the use of local probes is rendered difficult. In this work, a new method to study pitting corrosion on a MnS inclusion on 316L stainless steel is proposed. It consists in modifying locally the chemistry in its vicinity by injecting with a microcapillary an aggressive solution of NaCl, H2SO4 or HCl. Once a pit appears, scanning vibrating electrode technique (SVET) is used to follow the current fluctuations over and around the pit when the metal is polarized at a passive potential. In another series of experiments the effect of local activation of MnS inclusion was studied ex…

Laser heating and ablation at high repetition rate in thermal confinement regime

International audience; Laser heating and ablation of materials with low absorption and thermal conductivity (paint and cement) were under experimental and theoretical investigations. The experiments were made with a high repetition rate Q-switched Nd:YAG laser (10 kHz, 90 ns pulse duration and l = 532 nm). High repetition rate laser heating resulted in pulse per pulse heat accumulation. A theoretical model of laser heating was developed and demonstrated a good agreement between the experimental temperatures measured with the infrared pyrometer and the calculated ones. With the fixed wavelength and laser pulse duration, the ablation threshold fluence of paint was found to depend on the repe…

A New Insight in the Electrochemical Response of a Depassivated Surface

Influence of aeration on the localized trenching on aluminium alloys

This paper aims to make the difference between alcalinisation and micro-galvanic corrosion in the mechanism of the corrosion of Al alloys. Using a pH microprobe, the pH changes inside a pure water droplet deposited on a thermal aged 2011 aluminium alloy were scanned. These pH variations, depending on the position inside the droplet, were related to the heterogeneous corrosion attacks of the aluminium surface quantified by AFM measurements. A modelling investigation is proposed to evaluate the distinct roles of alcalinisation, due to the oxygen reduction reaction (ORR), and the galvanic coupling between intermetallic particles and the surrounding matrix. It can be concluded that the former c…

Laser cleaning of oxidized iron samples: The influence of wavelength and environment

A phenomenological laser-cleaning study of pure oxidized iron samples has been performed in order to model the influence of wavelength in air and the role of environment in the IR domain. Two sets of experiments were performed: (i) cleaning of oxidized specimens at different laser spot sizes and pulse numbers at wavelengths of 1064 nm and 532 nm in air and (ii) cleaning in air with electrolytes at 1064 nm for low energy densities.

Influence of the chemical dissolution of MnS inclusions on the composition of passive films and the local electrochemical behaviour of stainless steels

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.

Modelling and Diagnostic of Pulsed Laser-Solid Interactions Applications to Laser Cleaning: a TMR programme

This TMR programme ((ERBFMRXCT980188) aims to study the fundamental physical and chemical aspects of pulsed laser-solid interactions leading to any form of surface cleaning in order to develop the laser cleaning technique as a reliable industrial production tool.

Laser plasma plume structure and dynamics in the ambient air: The early stage of expansion

Laser ablation plasma plume expanding into the ambient atmosphere may be an efficient way to produce nanoparticles. From that reason it would be interesting to study the properties of these laser induced plasmas formed under conditions that are known to be favorable for nanoparticles production. In general, plume behavior can be described as a two-stage process: a “violent” plume expansion due to the absorption of the laser beam energy (during the laser pulse) followed by a fast adiabatic expansion in the ambient gas (after the end of the laser pulse). Plasma plume may last a few microseconds and may have densities 10−6 times lower than the solid densities at temperatures close to the ambie…

Towards a Study of Effects on Hydrogen Diffusion into T40 Titanium Alloys

In a global study of titanium alloys behavior in specific aqueous solution (embrittlement, corrosion and corrosion under stresses), the present work focuses on hydrogen diffusion into the metal and the consequences on its microstructure. Two ways of hydrogen charging were used to investigate this issue (gaseous and cathodic charging). The final aim is to determine a fitted method to create an identified microstructure and then to perform accelerated aging tests of titanium U-Bend samples into an autoclave with a specific environment. Hydrogen absorption and formation of titanium hydride have been studied by SEM analyses and by X-ray diffraction methods.

3 Probing and Modelling of Galvanic Coupling Phenomena in Localized Corrosion

The basic driving force of localized corrosion or corrosion protection in numerous cases is the galvanic coupling of which the dimensional aspect is fixed by a combination of scales regarding interfacial processes or properties. At the electrolyte–metal interface, it is necessary to consider the microstructure (including all real-time modification induced for example by applied stresses), the possible chemical changes at the surface of the material, and the electrolyte conductivity contribution, among others factors.

Simulation of abrasion–corrosion at high temperatures by in situ pulsed laser spallation of oxide films

Abstract A pulsed Nd:YAG laser combined with a thermogravimetric cell has been used to spall in situ the oxide films grown on a Fe–2.25Cr–1Mo steel at high temperature in oxidizing media. This technique allows to define the oxidation rate of bare metal surfaces, which can be used to simulate the corrosion-dominated regime during slurry–erosion tests.

A Mechanical–Electrochemical Approach for the Determination of Precursor Sites for Pitting Corrosion at the Microscale

International audience; The influence of metallurgical defects and residual surface stresses generated by polishing on the pitting susceptibility of duplex stainless steels was studied by combining macro- and microelectrochemical measurements with thermal-mechanical simulation and metallography tests. It has been shown that pits initiate in both phases at metallurgical point defects (such as oxide inclusions in the ferrite and dislocation lines in the austenite). By contrast, the surface stress state was the driving force for pit initiation along the austenite/ferrite interface. Experiments at the macroscale revealed that this process represents about 40% of the total number of pits observe…

Microstructural corrosion of aluminium alloys: a predictive finite element model based on corrosion-mimicking experiments

The purpose of this study is to implement the basis of a finite element model (FEM) based on the resolution of the Nernst–Planck equation in order to progress in the predictive simulation of microstructural corrosion on aluminium alloys. Certain constituent intermetallic particles at the surface of aluminium alloys are considered as preferential sites for the initiation of structural corrosion resulting in localised trenching around the particles and the surrounding Al matrix. In this work, a modified scanning electrochemical microscope (SECM) experiment was used to induce such phenomena via a local alkalinization on 200 nm thick aluminium coatings, promoting their local dissolution in an a…

Application du laser impulsionnel à l’étude de l’adhérence et de la structure des dépôts

Nous decrivons le signal acoustique enregistre a l’epicentre lors d’une activation laser dans le cas d’un materiau bicouche (acier inoxydable revetu d’alumine d’epaisseur 1,2 µm, 30 µm et 230 µm respectivement). Les resultats obtenus sont analyses en fonction de l’energie incidente et de l’epaisseur du depot. On a constate que le signal est fortement affecte par la presence du depot et que chaque regime d’interaction laser/materiau (thermoelastique, cloquage, expulsion) est caracterise par une reponse acoustique differente. Ceci nous amene a discuter des diverses applications du laser dans la caracterisation du depot et de l’interface substrat/depot. Il s’agit, par exemple, d’evaluer la con…

Laser depassivation of a channel flow double-electrode: A new technique in repassivation studies

Abstract A powerful tool for distinguishing between the different electrochemical steps involved during a depassivation-repassivation sequence was developed by combining the pulsed laser depassivation technique with an hydrodynamic electrochemical method: the channel flow double-electrode (CFDE). This experiment consisted of transporting the chemical species (Fe 2+ ) released by a depassivated iron electrode to a collecting electrode where these species were oxidized. A qualitative idea of the relative contribution of the anodic dissolution to the repassivation behavior was obtained. For a passive iron in acidic solution it was found that about 15% of the total charge is related to anodic d…

Local analysis of the mechanical behaviour of inclusions-containing stainless steels under straining conditions

Abstract A numerical method is described for determining the surface stress distribution under straining conditions from the real microstructure of materials containing local heterogeneities. The method is applied to resulfurized steels with a high density of MnS and oxide inclusions. The results are compared to those obtained from surface observations.

Laser fluence, repetition rate and pulse duration effects on paint ablation

Abstract The efficiency (mm3/(J pulse)) of laser ablation of paint was investigated with nanosecond pulsed Nd:YAG lasers (λ = 532 nm) as a function of the following laser beam parameters: pulse repetition rate (1–10,000 Hz), laser fluence (0.1–5 J/cm2) and pulse duration (5 ns and 100 ns). In our study, the best ablation efficiency (η ≅ 0.3 mm3/J) was obtained with the highest repetition rate (10 kHz) at the fluence F = 1.5 J/cm2. This ablation efficiency can be associated with heat accumulation at high repetition rate, which leads to the ablation threshold decrease. Despite the low thermal diffusivity and the low optical absorption of the paint (thermal confinement regime), the ablation th…

Modeling of Growth and Dissolution of Nanotubular Titania in Fluoride-Containing Electrolytes

In this paper, model calculations of diffusion processes and pH profiles inside TiO 2 nanotubes are performed in order to explore key factors in the growth mechanism of this system in aqueous electrolytes. An electrochemical steady state featured by an equivalent rate between oxide growth and dissolution is reached for a given current efficiency. Electrochemical oxide growth is found to be exclusively located at the pore bottom, whereas chemical oxide dissolution is uniformly distributed over the whole nanotube. It can be deduced from the results that electrolyte resistance or diffusion processes in the electrolyte inside the tubes are not limiting.

XPS and SIMS study of aluminium native oxide modifications induced by Q-switched Nd:YAG laser treatment

Publié suite au congrès ECASIA: 11th European Conference on Applications of Surface and Interface Analysis, 25-30 September 2005, Vienna, Austria; International audience; During laser cleaning of aluminium in ambient atmosphere, modifications of the metal surface can be induced by transient thermal effects. This work aims to characterize the modification of the aluminium oxide layer on pure aluminium for a wide range of power per area using a Q-switched Nd :YAG (1064 nm) laser with two pulse durations, 10 and 180 ns. Experiments were carried out with single laser shots in ambient air at fluences (e.g. energy per area) below the ablation regime. For 10-ns pulses with fluences between 0.7 and…

Localized hydrogen cracking in the austenitic phase of a duplex stainless steel

The aim of this study is to investigate the role of hydrogen on the mechanical behavior of an austenitic phase, in the particular situation of duplex stainless steels. In these duplex alloys, in presence of hydrogen, the ferritic phase is embrittled by hydrogen and the resistance to cracking is mainly related to the behavior of the austenitic phase. Thus, a discussion of the role of hydrogen at the crack tip of a duplex alloy (as function of the microstructure) has been proposed by T. Perng and C.J. Altester after experiments conducted in gaseous environment. A similar experimental approach has been followed in this study; slow strain rate tests (SSRT) have been performed on duplex stainles…

Consideration of the formation of solids and gases in steady state modelling of crevice corrosion propagation

Abstract One of the challenges in the simulation of crevice corrosion propagation is the rigorous treatment of non-aqueous species (gas or solids), since the appearance of a new phase in a crevice will automatically have an impact on its geometry. This paper presents a simple approach, where heterogeneous reactions are considered in a post-processing step, by determining the conditions of potential, external chemistry (pH, chloride, …) or geometry under which gas or solid phases could appear in the crevice. Thus, as function of these conditions, stability diagrams for the different phases that are liable to appear in an actively propagating crevice can be constructed. Such diagrams (e.g. di…

Depassivation Experiments by Laser‐Pulse‐Induced Spallation

Depassivation experiments have been conducted by applying a technique developed for adhesion tests. A laser-pulse-induced spallation of the passive film is induced in situ without any contact between the laser beam and the passive film. The depassivation is controlled by the short pressures induced at the metal-film interface. The interfacial stresses at the metal-film interface could be studied by this technique

Mapping the 3D-surface strain field of patterned tensile stainless steels using atomic force microscopy.

Abstract The quantification of microstructural strains at the surface of materials is of major importance for understanding the reactivity of solids. The present paper aims at demonstrating the potentialities of the atomic force microscopy (AFM) for mapping the three-dimensional surface strain field on patterned tensile specimens. Electron beam (e-beam) lithography has been used to deposit 16×16 arrays of gold-squared pads. Monitoring the evolution of such a pattern under applied strain allows to quantify the triaxial strains both at the micro-(plastic) domain and nanoscale (elastic) domain vs. applied strain. The proposed method was applied to stainless steels after 4.5% plastic strain.

Laser ablation of a turbid medium : Modeling and experimental results.

International audience; Q -switched Nd:YAG laser ablation of a turbid medium (paint) is studied. The optical properties (absorption coefficient, scattering coefficient, and its anisotropy) of a paint are determined with a multiple scattering model (three-flux model), and from measurements of reflection-transmission of light through thin layers. The energy deposition profiles are calculated at wavelengths of 532 nm and 1.064 $\mu$m. They are different from those described by a Lambert-Beer law. In particular, the energy deposition of the laser beam is not maximum on the surface but at some depth inside the medium. The ablated rate was measured for the two wavelengths and compared with the en…

Preliminary study on the laser cleaning of stainless steels after high temperature oxidation

Abstract The objective of the present work was to estimate the influence of pulsed laser irradiation on the removal of the oxide layer, which is developed on the surface of stainless steels during their exposure to high temperature oxidation. In general, this layer is a protective one, mainly against corrosion. However, in many manufacturing applications or maintenance work, the removal of the oxides is necessary; for example, the metallic surfaces should be cleaned before welding, otherwise the presence of oxides increases the tendency to brittle behaviour of the joint. In this study, a pulsed Nd:YAG laser (λ=1.064 μm, 10 ns) was used for the surface cleaning of three stainless steels with…