Showing papers in "Surface & Coatings Technology in 1988"

The use of scratch adhesion testing for the determination of interfacial adhesion: The importance of frictional drag

Abstract: For many years, despite a basic lack of understanding of the mechanics on which the test is based, the scratch adhesion test has provided a simple, rapid means of assessing the adherence of thin, hard wear-resistant coatings such as titanium nitride. Recently, some progress has been made on the modelling of the scratch adhesion test and these previously published models are critically reviewed. The test can be considered as a combination of (i) an indentation stress field, (ii) an internal stress field and (iii) a frictional stress field. The importance of each of these in determining the levels of adhesion for a number of titanium nitride/substrate systems will be discussed. In particular, the results obtained from changes in diamond stylus-coating (surface) interfacial friction (a frictional drag term) are presented and the apparent changes in coating-substrate adhesion (critical load Lc) which result are discussed.

A review of the methods for the measurement of coating-substrate adhesion☆

Abstract: Modern coating techniques now offer the possibility of modifying the surface of an engineering component to achieve improvements in both performance and reliability. One important and often overriding factor is the degree of adhesion between the coating and its substrate, and the aim of this paper is to discuss the methods which can be used to assess this critical property of the coating-substrate system. The advantages and disadvantages of each technique, e.g. the pressure-sensitive tape test, indentation testing, the scratch test, laser methods etc., are reviewed.

Fundamental studies associated with the plasma spray process

Abstract: More than 25 years ago, plasma spraying was established as a commercial process, but only recently have serious attempts been reported to establish a solid scientific base for this technology. The first part of this paper refers to the basic processes involved in plasma spraying, including plasma generation, plasma jet formation, particle injection, particle heat and momentum transfer, and particle deposition. In the second part, recent results obtained in this laboratory are summarized. These results are mainly concerned with the effects of vortex flow on particle motion and on air entrainment during atmospheric spraying.

Metastable coatings — Prediction of composition and structure

Abstract: New metastable materials can easily be obtained using low temperature vapour deposition techniques. These non-equilibrium materials have constant compositions and structures up to temperatures of about 0.3Tm (Tm, melting point; for hard substances approximately 2500 – 3000 °C) and therefore offer a variety of new coating materials with unknown properties. The compositions and structures of these vapour-quenched coatings can be roughly estimated from the equilibrium phase diagrams and more accurately from the free energies of the solution phases of the coating components considering diffusion coefficients, deposition rate and structural parameters. This paper gives an overview on the ideas and possibilities for predicting the compositions and structures of multicomponent coatings, especially for combinations between metallic and covalent hard materials. Coating experiments using (Ti, Al)N, (Zr, Al)N, (Hf, Al)N and other combinations are compared with the calculations of the compositions and structures in the corresponding stable or metastable systems. Agreement between experiment and prediction is found. The calculations are based on the estimated lattice stabilities of the different compounds in the various structures and the regular solution model with estimated interaction parameters.

Plasma source ion implantation: A new, cost-effective, non-line-of-sight technique for ion implantation of materials

Abstract: Surface modification by ion bombardment is a well-established technique for improving the hardness, friction, wear resistance and corrosion resistance of materials. Surface modification of materials by conventional ion implantation is a line-of-sight process in which a directed beam of energetic ions is rastered across a target. If the target is three dimensional, the process generally requires target manipulation to achieve uniform implantation over the entire surface of the object. This target manipulation requirement can seriously limit the cost effectiveness of ion implantation relative to more conventional surface treatments, especially for large and/or heavy targets. We are developing a new technique, plasma source ion implantation (PSII), which circumvents the line-of-sight restriction of conventional ion implantation. In PSII, targets to be implanted are placed directly in a plasma source chamber and are then pulse biased to high negative voltage (10 – 100 kV in our experiments). A thick, ion matrix sheath forms around the target, and ions accelerate through the sheath drop and bombard the target from all sides simultaneously without the necessity of target manipulation. Although the PSII process bears a superficial resemblance to existing techniques such as “ion plating”, “ion coating” or “plasma nitriding”, PSII produces a deposition profile characteristic of high energy ion implantation. Our experiments have demonstrated that PSII (1) efficiently implants ions to the concentrations and depths required for surface modification, (2) produces material with improved microhardness and wear properties and (3) dramatically improves the life of manufacturing tools in actual industrial applications. For example, in recent industrial field tests the tool life of M-2 pierce punches used to produce holes in mild steel plate has been increased by a factor of 70 – 80. In this paper we describe (1) the latest results from a series of ongoing field tests, (2) extensions of the PSII process to ion beam mixing and ion beam enhanced deposition modes of operation, and implantation of molecular ions, and (3) the comparative economics of surface modification by PSII relative to conventional ion implantation.

The scratch test - Different critical load determination techniques

Abstract: Different critical load determination techniques such as microscopy, acoustic emission, normal, tangential, and lateral forces used for scratch test evaluation of complex or multilayer coatings are investigated. The applicability of the scratch test to newly developed coating techniques, systems, and applications is discussed. Among the methods based on the use of a physical measurement, acoustic emission detection is the most effective. The dynamics ratio between the signals below and above the critical load for the acoustic emission (much greater than 100) is well above that obtained with the normal, tangential, and lateral forces. The present commercial instruments are limited in load application performance. A scratch tester able to apply accurate loads as low as 0.01 N would probably overcome most of the actual limitations and would be expected to extend the scratch testing technique to different application fields such as optics and microelectronics.

Preparation and behaviour of wear-resistant TiC/TiB2, TiN/TiB2 and TiC/TiN coatings with high amounts of phase boundaries☆

Abstract: The toughness of hard coatings is one important parameter influencing flank wear in metal cutting. Large amounts of phase boundaries can enhance the toughness of hard coatings. A method is described for producing coatings with large amounts of phase boundaries in the system TiC/ TiN/TiB2 by magnetron sputtering. The composition, properties and flank wear of these sequential coatings were examined during continuous and interrupted cutting. For the determination of the toughness of the hard coatings the crack propagation from Vickers' indentations and hertzian indentations was used. Coatings with 100 – 250 layers, with a total layer thickness of 5 μm, show optimum properties and performance.

The erosion-corrosion behavior of protective coatings☆

Abstract: The metal wastage caused by the impact of small solid particles on surfaces that are simultaneously corroded at elevated temperatures is a problem in several types of energy system. These systems cover a spectrum from heat exchanger tubes in fluidized bed combustors to steam turbine nozzles and blades. The use of protective coating systems of various kinds to extend the life of the components has been demonstrated to increase part life several times over. The behavior of various compositions and morphologies of coatings applied using several different processes in erosion and erosion-corrosion service environments is presented. The factors which determine their protective capabilities and the mechanisms by which they resist their operating environments are discussed. What is required of a coating system to be protective is defined.

Surface modification of medical implants and surgical devices using TiN layers

Abstract: The possibility of using titanium nitride as a wear-resistant coating for Ti6Al4V orthopaedic implants was investigated. TiN coatings were deposited with an arc technique under various cycle conditions to minimize the number of droplets incorporated during their formation. Pin-on-disc tests, scratch tests and metallurgical analyses were performed to characterize the more suitable TiN film in order to increase the hardness and the wear resistance in the articulating contact of the hip joints. With two different tribological systems, a pin-on-disc machine and a hip simulator, we have analysed and interpreted the wear mechanisms of the couples consisting of ultrahigh molecular weight polythylene against uncoated and TiN-coated Ti6Al4V prostheses. Wear test results indicated that the TiN film improves the surface hardness of Ti6Al4V implants. The polyethylene wear rate and the formation of TiO 2 abrasive particles are greatly reduced because of the low friction coefficient and good chemical stability of the TiN layer.

Ion flux characteristics in arc vapor deposition of TiN

Abstract: In this paper the ionization and energy characteristics of the particle flux impinging TiN films during arc vapor ion deposition are described. Langmuir probe measurements of voltage and current were made using a planar shielded substrate as the probe. Plasma species were observed using emission spectrometry. Substrate mass gain was measured as a function of voltage and nitrogen pressure. Ion current to the substrate was eliminated by applying a negative voltage to a fine wire screen located in front of the substrate and, at the same time, applying a positive voltage to the substrate. The ionized fraction of the titanium vapor at the substrate was determined by comparing the deposition rate obtained while excluding ions with the deposition rate obtained under normal conditions when ions were part of the depositing flux. The Langmuir probe measurements were used to estimate the plasma parameters and the average ion energy at the substrate. The results are as follows: (1) in the absence of a nitrogen gas discharge, the density of nitrogen ions is small; (2) most of the titanium vapor is ionized; (3) the average charge carried by titanium ions to the substrate during TiN deposition is (1.6 ± 0.3)e; (4) the average energy of titanium ions at the substrate is approximately 1.6e(10 + |Vs|) eV, where Vs is the negative substrate bias.

Deposition and properties of MoS2 thin films grown by pulsed laser evaporation

Abstract: Thin films of MoS2 have been grown on stainless steel substrates by pulsed laser evaporation. Analysis by X-ray photoelectron spectroscopy indicates that films grown at substrate temperatures up to 300 °C have the same stoichiometry as bulk MoS2; films grown at 450 °C are sulfur rich. The laser-deposited films have a granular structure and exhibit none of the dendritic structures typically observed in sputter-deposited films. Analysis of the films by X-ray diffraction indicates some preferred orientation. The coefficients of friction were measured in laboratory air and ranged from 0.09 to 0.25; the majority of values were between 0.16 and 0.20. These friction coefficients are in the appropriate range for a solid lubricant and indicate that pulsed laser evaporation is clearly a feasible technique for growing lubricious MoS2 films.

Adhesion strength of diamond films on cemented carbide substrates

Abstract: Diamond-coated cemented carbides are expected to be superior cutting tools for Al-Si alloys. For practical use in cutting, the adhesion strength of the diamond film is a major problem which could be improved. The adhesion strength of diamond particles, deposited by hot filament chemical vapour deposition (CVD) of CH4, was qualitatively measured in relation to the conditions of surface preparation of the carbide substrate and CVD. The adhesion strength is improved by deposition of diamond in pores formed by cobalt removal from near the surface of the substrate. Good adhesion is obtained when the size of the pore and the deposited particle is nearly equal. Better adhesion is obtained at a substrate temperature of 1000 °C compared with 800 and 900 °C. A diamond-coated carbide cutting insert was produced using the above results by microwave plasma CVD. The coating layer is mainly composed of diamond with a small amount of non-diamond carbon. The insert demonstrates a very small steady wear without flaking of the diamond film in cutting Al-10%Si alloy.

The relationship between structure and dielectric properties in plasma-sprayed alumina coatings

Abstract: Nine commercially available powders, with different morphologies, chemical compositions and particle size ranges, were plasma sprayed. The microstructures of the coatings obtained were analysed using optical microscopy and X-ray diffraction methods. The densities and open porosities were determined using hydrostatic weighing; they varied from 3.25 g cm -3 to 3.45 g cm -3 and 5.5% to 7.9% respectively. The volume resistivity of “assprayed” coatings were within the range of 10 9 – 10 10 Ω cm. Baking the coatings at 120 °C results in an increase in resistivity to 10 13 – 10 14 Ω cm. The dielectric constant at 1 kHz is in the range 5.9 – 8.3 depending on the kind of powder used and on the coating pretreatment. The loss tangent measured at the same frequency varies from 0.012 to 0.051. The dielectric strength of the coatings depends on the coating porosity and is in the range 90 – 180 kV cm -1 .

Residual stress and X-ray elastic constants in highly textured physically vapor deposited coatings

Abstract: It is well known that coatings made by physical vapor deposition are very strongly textured and, as a consequence, it is sometimes extremely difficult to measure the residual stress by the classical X-ray diffraction method A new goniometer has been developed where the diffraction pattern from the entire sample is integrated such that all peaks are recorded This permits a residual stress measurement to be made The instrumentation also allows phase analysis and pole figure determination In the present work, a number of highly textured TiN and Ti(CN) samples, taken from earlier studies, are investigated and these demonstrate the strengths of the new measurement technique Results are presented for the Ti(CN) film which show that the residual stress depends strongly on the diffraction peak chosen for study The dependence of the stress on the crystallographic orientation factor allows the X-ray elastic constants of the film to be derived These deviate from the theory and it is possible that this may not apply to highly textured samples which also have a stress gradient through the film

The abrasive wear resistance of sputter ion plated titanium nitride coatings

Abstract: Previous work has shown that under abrasive wear conditions it is not sufficient to consider coating hardness in isolation when seeking a guide to coating selection; it is more meaningful to talk in terms of the load-bearing capacity of the coating-substrate system. For titanium nitride coatings deposited onto austenitic stainless steel the variation in resistance to abrasive wear has been evaluated as a function of substrate bias voltage and the results have been compared with these earlier studies. Substrate bias has been identified as a particularly important system's parameter, since it allows some stress relaxation to occur within the coating because of its effect on porosity levels; this has important consequences with regard to adhesion, wear resistance and film hardness. With low substrate bias voltages, coatings degrade by a microchipping mechanism since fracture occurs relatively more easily in such open columnar microstructures, which are further characterized by low levels of internal stress accompanied by a poor load-bearing capacity. With increasing substrate bias much denser coatings are produced which result, initially, in better resistance to abrasive wear through increased load support. However, these improvements in coating microstructure result in higher levels of internal stress and these, when taken along with a reduction in the scratch adhesion critical load for failure Lc, eventually lead to a decrease in abrasive wear resistance with increasing bias voltage. The mechanism(s) by which the coatings degrade are described as a function of substrate bias, and the results are correlated with measurements of hardness, internal stress and critical load for coating detachment.

Chemical vapour deposition of a diamond coating onto a tungsten carbide tool using ethanol

Abstract: Diamond coating of a tungsten carbide alloy using the hot filament chemical vapour deposition process was investigated for application to tool manufacture. Previously, diamond deposition onto a cobalt-rich tungsten carbide alloy has been considered to be impossible using this process. However, it was found that using ethanol as the carbon source a good diamond coating layer could be obtained. Moreover, when a diamond-coated tool was applied to the shearing of an aluminium plate 2.5 mm thick, no abrasion of the diamond coating and no adhesion of chips of the sheared material to the tip of the tool were found even after 5 × 10 4 punchings, demonstrating the excellent hard coating effect as well as reasonably good adhesion of the coated diamond layer.

Thick compact MoS2 coatings

Abstract: Compact non-columnar coatings of MoSx with a thickness of up to 25 μm were deposited by d.c. as well as r.f. magnetron sputtering in argon at low pressure (about 1 mTorr) onto polished AISI 440C steel discs, Si(100) wafers, glass and polished polycrystalline Al2O3. They showed superior properties to the well-known MoSx coatings deposited at gas pressures about one order of magnitude higher.

Hard coatings for decorative applications

Abstract: Reactively deposited films of TiN and ZrN are of great interest as decorative coatings and in architectural glass applications. Traditional methods of film deposition have posed problems related to available deposition rates, film quality and color control. The cathodic arc plasma deposition process offers an alternative to deposit such films with good uniformity, film quality and color control. This paper deals with hard coatings for decorative applications deposited using the cathodic arc process. The films of TiN, ZrN, HfN, TiAlN and TiZrN are characterized in terms of structure and morphology, colorimetric and optical reflectance, hardness, wear resistance and corrosion resistance. It is demonstrated that by adjusting process conditions, doping with carbon and/or alloying with other elements it is possible to adjust coating colors over a wide range and to simulate closely a range of gold colors. The cathodic arc therefore provides a significant alternative to existing techniques for a wide range of decorative applications.

Residual stresses in ZrO2-8%Y2O3 plasma-sprayed thermal barrier coatings

Abstract: The successful application of zirconia as thermal barrier coatings in the combustion chamber of diesel engines is dependent on their achieving adequate thermal shock resistance and resistance to attack by combustion gases. Of particular importance is the control of residual stresses in the ceramic coatings if useful lifetimes are to be achieved. An experimental technique for the determination of residual stresses is described, and the effect of varying spraying parameters such as deposition rate and air cooling, and the presence of a bondcoat, are discussed.

Structure of Titanium Nitride coatings deposited by physical vapour deposition: A unified structure model

Abstract: Although a number of studies have been published regarding the structure of physically vapour-deposited titanium nitride coatings, no unified structure model has yet been proposed which accounts for all experimental observations. The results of positron annihilation, X-ray diffraction (on both adherent and free-standing films) and scanning electron microscopy studies, performed both before and after tempering, on titanium nitride film deposited by low rate d.c. sputtering, high rate magnetron sputtering and reactive ion plating have been combined to give a unified structure model. The various contributions to both macrostrain (macrostress) and microstrain (microstress) are discussed as a function of the processing variables (substrate bias, deposition rate etc.) for each of the physical vapour deposition processes. In particular, the model can account for the high lattice parameter of physically vapour-deposited titanium nitride coatings and the variation in unit cell dimension of the nitride with deposition rate and substrate bias voltage.

Nucleation and growth phenomena in chemically vapor-deposited diamond coatings

Abstract: The deposition of crystalline diamond coatings by microwave plasma-assisted chemical vapor deposition (CVD) is the main subject of this paper. The plasma is excited in a hydrogen-rich methane and hydrogen mixture with a substrate temperature of approximately 1000 °C. High chemical reactivity of the plasma limits the application of the CVD process to certain substrates. Autoepitaxy of diamond on diamond substrates has already been demonstrated, but nucleation of diamond on non-diamond substrates creates many conceptual and practical problems. Experimental observations of the nucleation of diamond on various substrates are presented and discussed. Several phenomena are connected with the growth mechanism of diamond: competition in nucleation between diamond and graphite, surface activity of the species, adsorption and desorption of hydrogen on the diamond surface and surface reconstruction. In turn, a collective interaction between the plasma, the growing surface and the bulk substrate is expected to be responsible for the observed maximum growth rate at approximately 1000 °C and the narrowing of the other process parameters. These delicately balanced interactions provide conditions for growing relatively perfect crystalline diamond films. The other issue is how to achieve a high growth rate of diamond. One approach is by a catalytic growth mechanism in which an intermediary role is played by some atoms such as boron, silicon, titanium and others. Growth of diamond films on titanium substrates may reach rates of up to 20 μm h-1.

Technical note: Grit blasting as surface preparation before plasma spraying☆

Abstract: One of the major reasons for grit blasting before plasma spraying is to create enough surface roughness to ensure a strong mechanical bond between coating and substrate. However, this treatment also leaves a certain amount of grit residue, normally referred to as contamination, trapped in the surface. These residues are known to weaken the adherence of the coating, especially for those coatings operating at high temperatures and exposed to mechanical loading. The current work presents a total survey of the influence of grit-blasting parameters (automatic equipment) on surface roughness and contamination level for various alloys. Surface roughness was determined by using traditional measuring techniques whereas a method for measuring contamination levels with X-ray spectrometry was developed. The latter were correlated with the results of point counting in an optical microscope. It was found that maximum surface roughness is obtained at a stage where the contamination level increases rapidly. By using the above survey the grit-blasting parameters for the adherence of a plasma-sprayed Co-Mo-Cr-Si alloy on Inconel 718 were studied. The assessment of adherence was made using an improved tensile bond strength test method for both “as-coated” samples and samples exposed to simulated service conditions.

Evaluation of existing ion plating processes for the deposition of multicomponent hard coatings

Abstract: Physical vapour phase deposition processes have successfully expanded into the field of coatings against wear and friction. The different ion plating processes developed so far are compared with respect to their significant characteristics and their ability to deposit TiN coatings onto different materials and onto tools of different sizes. The suitability of the established processes for depositing the multicomponent and multilayer coatings now being developed is discussed. In a series of coating experiments the most flexible processes using the magnetron sputter source and the arc evaporation source are compared for their ability to deposit films of the ternary compounds Ti x Al 1 − x N.

Electrochemical and thermochemical boriding in molten salts

Abstract: Research into the electrochemical and thermochemical boriding of steel substrates revealed that the process of boride layer formation is controlled by the diffusion of boron into the substrate. The rate of growth and the phase composition of the layer are determined by the activity of boron on the surface, the temperature and the composition of the substrate. The composition of the boriding medium is irrelevant to the rate of growth and the phase composition of the boride layer in electrochemical boriding but is of primary importance in the thermochemical process. The boride layers formed in the electrolytic boriding generally consist of two phases: FeB and Fe2B. In the thermochemical boriding, the formation of the FeB phase can be partially or entirely suppressed. When a boride layer is grown on high-alloyed steels, most alloying elements form a diffusion barrier which slows down the rate of the boride layer formation and increases the content of the FeB phase. This may be avoided by boriding iron-coated high-alloyed steel substrates.

The effects of hertzian stress and test atmosphere on the friction coefficients of MoS2 coatings

Abstract: R.f. sputter-deposited MoS2 coatings on 304 stainless steel substrates have been evaluated for different deposition and different storage conditions. For air testing, the friction coefficients of all the MoS2 coatings decreased with increasing hertzian stress up to an intermediate stress and were constant for still larger stresses. Lower friction coefficients were observed for samples stored in the lower (2% in comparison with 98%) relative humidity atmosphere. In addition, the constant friction coefficients with increasing stress were initiated at a lower hertzian stress for storage at 2% relative humidity. The MoS2 films were predominantly crystalline; however, a small amount of amorphous material was present. The coatings containing the larger amounts of amorphous material had the larger friction coefficients. Testing in ultrahigh vacuum lowered the friction coefficients relative to testing in air for both relative humidities; however testing in ultrahigh vacuum did not recover all of the increase in the friction coefficients for air testing that was attributed to high humidity storage. The coatings contained all orientations, but the basal planes were predominantly perpendicular to the substrate surface. The sulfur-to-molybdenum ratio did not decrease significantly with high humidity storage, as has been observed by others for similar storage conditions, although the crystallographic orientation of the films was similar. Hence, these results indicate that factors in addition to orientation affect the oxidation of MoS2 films.

Internal stress in titanium nitride coatings: modelling of complex stress systems

Abstract: The internal stress in sputter-ion-plated titanium nitride coatings has been measured by the well-known sin2ψ method. In such measurements it is usual to assume that the true stress state approximates to a biaxial state which requires that there is a linear variation in lattice strain with sin2ψ. However, this is not always the case, and it is shown that appreciable errors in the calculated values of the principal stresses σ11 and σ22 result if effects such as ψ splitting and curvature in the eφψ vs. sin2ψ plots are ignored. Results are presented which compare the values of stress calculated using the simple biaxial approximation with those obtained from a more detailed analysis. As these physical-vapour-deposited coatings thicken it is shown that the levels of internal stress decrease owing to a combination of grain size and porosity effects. These changes in coating microstructure cause curvature in the eφψ vs. sin2ψ stress plots and the stress state can be modelled by assuming that the stress varies exponentially with coating thickness.

Fracture toughness of plasma-sprayed zirconia coatings

Abstract: Plasma-sprayed ceramic coatings are formed by introducing a powder into a plasma jet to produce a stream of molten particles which then impact, spread and rapidly solidify onto a substrate to form a lamellar microstructure. The cohesive and adhesive fracture toughness of zirconia coatings, fully or partially stabilized with Y2O3 or CeO2, plasma sprayed onto steel, have been determined using the double cantilever beam (DCB) technique. The results show that cohesive fracture toughness is greater than adhesive toughness and that tetragonal coatings have significantly higher toughness than fully stabilized (cubic) zirconia coatings. The highest toughness was achieved with ZrO2-CeO2 coatings which contained a significant proportion of transformable tetragonal phase. The results are interpreted in terms of the influence of grain size and composition on the tetragonal-to-monoclinic phase transformation.

A magnetron sputter ion plating system

Abstract: A new type of system for the deposition of hard coatings on cutting tools has been designed, constructed and tested The system is based on the well-established principles of magnetron sputter source ion plating but uses a long narrow cylindrical chamber with three magnetrons running the full length of the chamber This geometry is such that all samples are in the same coating and plasma environment, ensuring uniformity of thickness, adhesion, stoichiometry and structure of the coating over the surface of each sample and for all samples It also results in a very efficient use of chamber volume, fast pumpdown, fast deposition times and therefore high productivity

Corrosion behavior of chromized and/or aluminized 214Cr-1Mo steel in medium-BTU coal gasifier environments

Abstract: The corrosion behavior of 214Cr-1Mo steel with various coatings was investigated in a simulated, medium-BTU, coal gasifier environment at 600 °C. Aluminized coatings were found to be unsuitable for use in coal gasifier atmospheres because they experienced severe cracking and internal sulfidation-oxidation. Chromized coatings with more than 30 wt.% Cr and a coating thickness of 120 μm provided acceptable corrosion resistance. However, further improvement in scale adherence is essential for long-term service. Sulfidation of base metal constituents at the coating surface and internal oxidation-sulfidation degraded the chrome-aluminized 214Cr-1Mo steel and breakaway corrosion occurred.

Influence of anions on the passivity behavior of copper in alkaline solutions

Abstract: The competitive effect of the inorganic anions OH-, Cl-, Br-, I-, ClO-4, NO-3, SO2-4, CO2-3 and phosphates on the behavior of copper in alkaline aqueous solutions at pH 12 was investigated. The nature of changes occurring on the copper surface was analyzed by potentiodynamic and potentiostatic methods in conjunction with different instrumental surface analysis techniques. The influence of these anions on the anodic dissolution of copper was classified into three distinct categories. In the first group, comprising NaCl, NaBr and NaI solutions, copper(I) salts form insoluble, nonprotective films on the metal surface and the copper is expected to dissolve via the formation of CuA( n - 1 )- n complexes. In the second group, comprising NaClO4, Na2SO4 and NaNO3 solutions, substantial dissolution of copper is caused by the formation of easily soluble Cu2+ salts, and copper (II) ions precipitate as hydroxides and oxides. In the third group, the hydroxide, phosphate and carbonate passivate the copper surface. In some solutions the phosphate and carbonate inhibit the anodic dissolution of copper. The aggressive nature of the anions investigated against the passivity of copper increases in the order SO2-4