Tribocorrosion is an irreversible transformation of a material resulting from simultaneous physicochemical and mechanical surface interactions taking place in a tribological contact. Tribocorrosion involves numerous synergy effects between mechanical and chemical or electrochemical phenomena. In the present paper a general framework for the interpretation of electrochemically controlled tribocorrosion experiments involving a sliding contact between a passive metal and an inert counter body is proposed. The analysis is based on material fluxes and takes into account the formation, transformation and ejection from the contact of third body particles. The usefulness of the proposed approach is illustrated with examples from the author’s laboratory.

The tribocorrosion behaviour of a passive AISI430 ferritic stainless steel sliding against alumina in 0.5M sulphuric acid has been studied using a tribometer that allowed for electrochemical measurements. The effects of applied potential, normal load, sliding velocity, sliding distance and alumina roughness on the friction, wear volume and anodic current were determined. The obtained results are interpreted in terms of a previously proposed theoretical model describing the average current in terms of depassivation rate and repassivation charge, taking into account the role of non-electrochemical parameters such as applied normal force, sliding velocity, metal hardness and contact configuration. Under the experimental conditions of the present study, the depassivation rate was found to govern the measured anodic current. Consideration of how mechanical and operational parameters affect the depassivation rate led to a consistent description of their effect on the tribocorrosion rate in accordance with the proposed model.

Based on previous research using a UBM laser profilometry technique that proved successful in recognizing and quantitatively documenting different wear polishes on stone tools used to work different contact materials and the identification of a fractal dimension (Dr) on some used tool surfaces, additional experiments using the same technique have been undertaken to elaborate upon this work. The focus of these experiments using the same technique concerns the study of wear polish development and associated changes in stone surface microtopography. Questions relating to the stage at which the first identification of different contact material polishes is possible and when the fractal dimension (Dr) is manifested on tool surfaces are investigated.

The effect of electrode configuration on the tribocorrosion behavior of a ferritic stainless steel in sulfuric acid solution was investigated. A truncated cone was rubbed against a stationary plate using a reciprocating motion pin-on-plate tribometer under potentiostatic control. Three contact configurations were investigated consisting of a ceramic pin rubbing on a steel plate (I), a steel pin rubbing on a ceramic plate (II), and a steel pin rubbing on a steel plate (III). The instantaneous current during each stroke and the evolution of the average current during an experiment were monitored. The total metal removal rate was measured by laser profilometry, the wear scar morphology was investigated by scanning electron microscopy and the electrochemical contribution to total wear was calculated from the measured anodic current using Faraday’s law. The results show that the electrochemical technique yields useful results for all three contact configurations including the metal–metal contact. The total wear volumes for configurations (I) and (II) were found to be comparable. The current transients suggested that the rate of metal loss was governed by the rate of mechanical depassivation. The total wear volume for configuration (III) was highest because of the larger metallic surface area and because of severe adhesive wear.

The degradation of DIN 34CrNiMo6 steel sliding against alumina was investigated in NaOH and in borate buffer solutions of PH 8.4 under electrochemically applied passive potentials. Small amounts of chromate or chloride were added to the borate solutions to vary the nature of the passive film. Film thickness and composition were characterised using surface analysis (Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS)). For comparison, tribocorrosion experiments were carried out at appropriate applied cathodic potentials, where no iron oxidation is thermodynamically possible, and therefore no passive film is formed.Results show the crucial role played by surface oxidation not only with respect to wear accelerated corrosion processes but also on surface mechanical phenomena. Depending on the nature of the solution, passive carbon steel exhibits either subsurface cracking or plastic flow accompanied by wear. In absence of passive film, wear is negligible and large plastic flow of the metal occurs, independent of the nature of the solution. (C) 2001 Elsevier Science B.V. All rights reserved.

The electrochemical contribution to tribocorrosion, wear accelerated corrosion, has been studied with a view to improving the understanding of the mechanisms involved. The measured current during tribocorrosion has been interpreted in terms of the ohmic resistance, the applied potential and the position of the working electrode. Results showed that a much better estimate for the ohmic resistance, in a tribocorrosion system, can be obtained by direct measurement using electrochemical impedance spectroscopy, as opposed to an independent electrochemical test. An increase of the applied potential in the passive range led to an increase in anodic current and overall material loss. The effect of potential on tribocorrosion can be related to repassivation kinetics but the depassivated and not nominal are must be considered. The position of the electrode in tribocorrosion was shown to affect its electrochemical response. The use of a metal pin sliding against an Al2O3 plate led to crevicing due to an IR-induced potentialdrop.

Tribocorrosion is an irreversible transformation of a material resulting from simultaneous physico-chemical and mechanical surface interactions in a tribological contact. Electrochemical methods are well suited for the study of tribocorrosion phenomena because they allow one to simulate the corrosive effect of the environment by imposing a fixed potential. Furthermore, the measurement of the anodic current permits one to determine the amount of material removed by oxidation as opposed to mechanical wear. In the present paper, experimental and theoretical aspects of applying electrochemical methods in tribology are discussed and recent results obtained with passivating metals in the authors' laboratory are presented. The importance of controlling the mechanical parameters and the contact geometry is stressed, and it is shown that these parameters can significantly affect the electrochemical response of a tribocorrosion system.

Lithic use-wear analysis, despite being a well-accepted research tool, is still undermined by its qualitative nature. An effort has been made to quantify use-wear analysis, but only with limited success. This paper will present a new method of analysis based on a non-destructive measurement technique, laser profilometry. This optical technique, when coupled with appropriate software, allows for easy measurement of roughness parameters at several length scales. This accounts for the length-scale dependence of surface topography and allows for its quantitative description. Further, the information from this type of measurement can, in some cases, be described by fractal geometry leading to new interpretive possibilities. Initial results showed that measurements could be made on several different chert and obsidian samples and that these could be distinguished based on their wear histories.