Effect of electrode potential on the tribocorrosion of tungsten

The tribocorrosion behavior of tungsten sliding against an alumina ball was evaluated in sulfuric acid under applied electrode potential. Surface chemistry of worn and unworn surfaces was evaluated using XPS and AES. Quasi-potentiostatic polarization curves and potential step measurements were performed under mass transport control to assess relevant corrosion factors. It was found that the tribocorrosion rate of tungsten varies with the applied electrode potential and goes through a maximum for a potential of 0.5 V MSE. Different material removal mechanisms were identified. In the wear track, materials deterioration proceeds by cyclic mechanical removal of the passive oxide film followed by anodic oxidation. The removal rate was found to be proportional to the passivation charge density determined in independent electrochemical experiments. At higher potential (1 V MSE) a thick WO₃ tribolayer forms and by covering the wear track reduces the tribocorrosion damage. Outside the wear track the stirring of the solution induced by the moving alumina ball leads to an enhancement of the dissolution rate of the WO₃ passive film and thus to higher material wastage.     

Tribocorrosion of Pulsed Plasma-Nitrided CoCrMo Implant Alloy

In the present study, a forged CoCrMo (ISO 5832-12) has been subjected to pulsed plasma treatment in a N₂/H₂ atmosphere at low temperatures (below 500 °C). This treatment resulted in the formation of a layer composed by dispersed chromium nitride particles in a N-enriched metal matrix. The materials were tested for corrosion and tribocorrosion performance in 0.9 wt% NaCl at room temperature under controlled electrochemical conditions. After the treatment, the alloy loses its passive nature. The electrode potential was found to critically affect the corrosion and the tribocorrosion rates. In the nitrided alloy, a significant increase of corrosion rate was found at high potentials, while tribocorrosion was determined mainly by mechanical wear and not affected by potential. On the other hand, the untreated CoCrMo alloy exhibited stable corrosion over a wide range of potentials. Its tribocorrosion rate was similar to the nitrided alloy samples at low potentials, but it increased dramatically at high potentials where passivity triggered severe wear-accelerated corrosion and promoted mechanical wear. The present study shows that the electrochemical conditions determine material deterioration and should therefore be considered when selecting materials for tribocorrosion applications such as biomedical implants.     

Electrochemical Effects on the Corrosion-Wear Behaviors of NiCrMo-625 Alloy in Artificial Seawater Solution

In this article, the tribocorrosion behaviors of NiCrMo-625 alloy sliding against an Al₂O₃ pin using a pin-on-disk tribometer have been carried out to assess the effect of electrochemical state on the corrosion–wear properties of the alloy in artificial seawater. The results shows that a cathodic shift in the open circuit potential of NiCrMo-625 alloy during tribocorrosion is confirmed and a marginal increase in corrosion current can be found under tribocorrosion compared to static corrosion. Total material loss of NiCrMo-625 alloy during tribocorrosion obviously increases with an increase in applied potential, indicating the synergistic effect between wear and corrosion. Although the corrosion rate of the alloy is significantly increased by sliding, the ratio of wear-induced corrosion to the total wear loss is not very large. The proportion of wear-induced corrosion and corrosion-induced wear to the total material loss increases obviously with an increase in potential.     

Friction and Wear Characteristics of Single Crystal Ni-Based Superalloys at Elevated Temperatures

The purpose of this study was to investigate the friction and wear behavior of single crystal superalloys at elevated temperatures. Pin-on-plate experiments were conducted using a custom-built high-temperature fretting/wear apparatus. Measurements were performed on two single crystal Ni-based alloys and Waspaloy^® (used as a baseline material). The coefficient of friction for the single crystal materials (i.e., during running-in and steady state) was lower compared to the Waspaloy^®. In addition, the experiments showed that the friction coefficient of the single crystal is dependent on the crystallographic plane; the friction coefficient was lower for the tests on the {100} plane compared to the {111} plane. The wear behavior was aligned with the friction behavior, where the single crystal Ni-based alloys showed slightly higher wear resistance compared to the Waspaloy^®. Ex situ analysis by means of FIB/SEM and XPS analysis revealed the formation of Co-base metal oxide layer on the surface of the single crystal alloy. Similarly, a Co-base oxide layer is observed on the counterface providing a self-mated oxide-on-oxide contact and thus lower friction and wear compared to the Waspaloy^®.     

Wear and tribocorrosion behaviour of 304L stainless steel welds

The influence of the microstructures of the base metal and weld metals on the wear and tribocorrosion properties of 304L stainless steel (SS) welds prepared by Manual Gas Tungsten Arc Welding (M-GTAW) and Activated Flux Gas Tungsten Arc Welding (A-GTAW) processes are reported. Increase in sliding speed increased both friction forces as well as wear rate. Higher hardness in M-GTAW weld metal resulted in increased wear resistance than A-GTAW weld metal and base metal. The inferior wear resistance of the base metal was due to the strain hardening behaviour under sliding condition. The polarization curves showed increase in passive current density under sliding condition. The applied potential was found to influence the tribocorrosion resistance of the material. Under tribocorrosion condition, the total material loss was higher in base metal followed by A-GTAW weld metal and M-GTAW weld metal. Characterization of worn surface by SEM indicated a mixed wear mechanism of abrasive and adhesive wear. The worn surface appeared relatively smoother in nitric acid medium than in dry condition. The influence of microstructure affecting the hardness, wear and tribocorrosion resistance of the base metal and weld metals of 304L SS is discussed.     

Assessing the Tribocorrosion Performance of Three Different Nickel-Based Superalloys

Tribocorrosion, which is a material deterioration caused by the synergistic effect of corrosion and wear acting together, is encountered in many engineering applications. Ni-based superalloys, which are widely used in chemical, petrochemical and nuclear power industries as well as in hot sections of turbine engines, owing to their excellent corrosion resistance, high strength and capability to retain hardness at elevated temperatures, are subjected to corrosive wear in service conditions. Therefore, an understanding of the tribocorrosion behavior of these superalloys allows choosing the right material for specified applications and predicting the material damage. In this study, the tribocorrosion behavior of Hastelloy C2000, Hastelloy G35 and Haynes 625 was studied using different electrochemical test techniques including open circuit potential (OCP) measurement, potentiodynamic and potentiostatic polarization tests under sliding contact in 3.5 wt% NaCl solution. Scanning electron microscopy (SEM) was employed in order to characterize corrosive-wear damage, and the surface profiles of wear tracks were obtained using a high-resolution surface profilometer for calculating wear loss. Also the metal dissolution caused by corrosive wear was detected using an inductively coupled plasma optical emission spectrometer (ICP-OES). Test results indicated that the tribocorrosion performance of superalloys is affected by their elemental composition and microstructural characteristics, which induce changes in mechanical properties. Haynes 625, which has the highest hardness value owing to decreasing grain size, showed less material volume loss than other superalloys in all tests. However, the protective oxide film on Haynes 625 especially thickened in potentiodynamic tests provided inhibition of excessive metal dissolution. Cathodic protection resulted in decreasing material loss, but on the other hand hydrogen intake was observed on cathodically polarized specimens.     

Tribocorrosion behavior of Ti–C–O–N nanostructured thin films (black) for decorative applications

In the past few years, tribocorrosion has become a focus of research because of its relevance in terms of the future in-service degradation mechanisms of materials. In the particular case of decorative coatings, tribocorrosion is certainly one of the most important issues, and sweat corrosion and human contact wear are two other factors that may act as material selection tools.Thus, the current study aimed to investigate the tribocorrosion behavior of a new class of thin films, the Ti–C–O–N system, which is being developed to be used as a surface decorative material due to its relatively dark appearance. The films were prepared by reactive magnetron sputtering. The influence of the structural features on the tribocorrosion behavior is discussed.     

Triboelectrochemical techniques and interpretation methods in tribocorrosion: A comparative evaluation

Tribocorrosion is a material deterioration or transformation resulting from simultaneous action of wear and corrosion. Tribocorrosion is found in many engineering applications but the involved mechanisms are still little understood. The investigation of tribocorrosion requires the control of the chemical conditions during a wear test. In aqueous electrolytes, this is achieved by using different types of electrochemical-controlled wear experiments (triboelectrochemical experiments). This paper presents a critical appraisal of the main electrochemical techniques and evaluation methods used in tribocorrosion research with special emphasis on sliding and fretting situations involving passive metals.     

Tribocorrosion of Stellite 706 and Tribaloy 400 superalloys

Abstract

Co based superalloys such as Stellites and Tribaloys have been extensively used in many engineering applications owing to their inherent superior corrosion and wear resistance and hot hardness property at elevated temperatures. The combined interaction among wear and corrosion which is known as tribocorrosion often results in a significant increase in material loss especially in aqueous environments. In this study tribocorrosion performance of Stellite 706 and Tribaloy T400 was investigated by electrochemical techniques such as potentiodynamic (anodic polarisation) and open circuit potential (OCP) measurement with three electrode electrochemical cell set-up under sliding contact in 3·5% NaCl solution. The effect of friction on anodic polarisation behaviour of superalloys was studied at different loads of 20 and 80 N. During OCP measurements the frequency was increased from 0·5 to 1·5 Hz by an increment of 0·5 Hz. Thus the effect of frequency on tribocorrosion behaviour of superalloys was determined. Tribaloy 400 exhibited greater performance in potentiodynamic polarisation test. On the other hand, Tribaloy 400 was more affected by corrosive wear in OCP measurements as compared to Stellite 706.     

Influence of current impulse on machining characteristics in EDM

Electrical discharge machining (EDM) is a machining process transforming electric energy into thermal energy to remove materials. The current impulse is a very important factor for machining characteristics of EDM. A series of experiments were performed to investigate the influence of current impulse on machining characteristics. The features of current impulse have initial current, current rising slope and impulse pattern. The used patterns of current impulse included rectangular current impulse, trapezoidal current impulse and the 1^st order current impulse. The machining characteristics are associated with relative wear ratio (RWR) and material removal rate (MRR). Experimental showed that using trapezoidal current impulse with small initial current or little current rising slope reduced relative wear ratio and material removal rate as well. However, larger relative wear ratio was obtained for workpiece of tungsten carbide when current rising slope was too little. Using the 1^st order current impulse with 20 μs current rising time can improve relative wear ratio about 30 % while remain material removal rate the same as rectangular current impulse for tungsten carbide.     

A Pin-on-Disc Study on the Wear Behaviour of Two High-Performance Railway Wheel Steels

The wear behaviour of two railway wheel steels, ER8 and SUPERLOS^®, was studied through pin-on-disc tests, and the results were correlated with those previously obtained with twin-disc tests. The work-hardening of the steels was investigated with Vickers hardness measurements, and the wear mechanisms were studied using scanning electron microscopy. ER8 discs showed higher wear resistance, lower work-hardening ability and less wear damage than SUPERLOS^® ones, confirming the results of the twin-disc tests. Therefore, sliding pin-on-disc experiments are recommended as a simple laboratory technique that can be used as a screening method for wheel steel performance prior to more complex and more expensive tests. The damage in both steels was due to the concomitance of oxidative wear, abrasive wear and fatigue wear. Iron oxide formation protects the steels from severe wear, whereas its detachment causes abrasive wear; furthermore, surface fatigue cracks initiate and propagate leading to the detachment of material flakes.     

Influence of the Erodent Shape on the Erosion Behavior of Ductile and Brittle Materials

Solid particle erosion is identified as a major wear process occurring in numerous industrial applications. A number of test parameters influence the behavior of the materials during this wear process. Particle shape is one of the key factors, which is often discussed for ductile or brittle materials in the literature, but a comparative study of ductile and brittle materials showing an effect of particle shape has not been addressed in detail until now. The present work discusses the influence of erodent shape on the wear behavior of a ductile (Ti-6Al-4 V alloy) and a brittle (TiN coating) material during the erosion process. Investigations are performed in an erosion test rig where the ductile and brittle materials are charged with spherical and angular SiO₂ particles at normal impact. Results show an inverse erosion behavior of ductile and brittle materials with the variation in particle shape. Ductile materials show low material removal with spherical particles, whereas brittle materials show low material removal rates with angular ones. This work also provides an analysis of the material removal phenomenon to understand the effect of particle shape on tested materials. Since materials removal phenomenon in ductile materials is often reported in the literature, this work addresses the material removal behavior especially in ceramic coatings.     

On the Tribocorrosion Responses of Two Stainless Steels

Tribocorrosion has considerable effects on AISI 304L used in olive processing equipment. In fact, some investigations have been conducted to compare the tribocorrosion behavior of AISI 304L to UNS 2205 stainless steels sliding against alumina in olive pomace–tap water filtrate. The active and passive surface states involved in tribocorrosion mechanisms of the steels have accordingly been analyzed. Mechanical and corrosion wear components were quantified. It was revealed that the tribocorrosion mechanism was dominated by mechanical removal. The mechanical resistance of UNS 2205 proved to be more important than that of AISI 304L. Furthermore, UNS 2205 was more sensitive to corrosion under sliding than AISI 304L due to its two-phase microstructure.     

Tribocorrosion modeling of stainless steel in a sliding pair of pin-on-plate type

In this paper, the results of research into tribocorrosion wear of three types of stainless steel: AISI 430, 304 and 420 are presented. The research was carried out on a pin-on-plate stand in a 0.5 M solution of H₂SO₄. The aim of the research was to define relations between original properties of steel (resistance to abrasion and corrosion) and the intensity of tribocorrosion wear.Moreover, the authors present their own computational model allowing to forecast the effects of tribocorrosion in pin-on-plate type combination. As concerns forecasting the intensity of tribocorrosion, the authors state that maximum differences did not exceed 15%.     

TiCxOy thin films for decorative applications: Tribocorrosion mechanisms and synergism

Recently, tribocorrosion is widely accepted as an interdisciplinary area of research and such studies on various materials are gaining more attention by scientists and engineers due to its practical and economical significances in a wide range of applications. The main objective of the present work were to investigate the tribocorrosion behaviour of single layered titanium oxycarbide, TiC_xO_y, thin films on a reciprocating sliding tribometer, and in the presence of artificial sweat solution at room temperature, by considering the practical usage of such films as a decorative coating on various components.

The films were produced by DC reactive magnetron sputtering, using C pellets incrusted in the Ti target erosion area. A gas atmosphere composed of Ar and O₂ was used. The Ar flow was kept constant, and the oxygen gas flow varied from 0 to 10 sccm. During the wear tests both the open circuit potential and the corrosion current were monitored. Also, electrochemical impedance spectroscopy (EIS) tests were performed before and after sliding process. The modifications on the “native” coating microstructure and/or chemical composition induced by the variation of the deposition parameters were also evaluated and correlated with the wear–corrosion mechanisms occurring in each system.

The corrosion studies, including EIS measurements, exhibited the high corrosion resistance of the TiC_xO_y films, which is clear from the unchanged/constant values of the polarization resistance, before and after the sliding process, at the evaluated potential. The effects of hardness, thickness and structure of the films on their tribocorrosion performance, as a function of oxygen fraction, were studied and an attempt was made to classify them. Two of the eight films (f_O=0.55 and 0.79), considered in the test, demonstrated better tribocorrosion resistance than others. Further, individual and synergistic effects of wear and corrosion on total wear loss were estimated and correlated with tribocorrosion mechanisms.     

Time Dependence of Tribocorrosion Behavior for Stainless Steel and Alumina Tribocouples in Seawater

Tribocorrosion is an important phenomenon encountered in many practical engineering situations, resulting in accelerated materials degradation and serious economic losses. In this work, pin-on-disk friction experiments were carried out in seawater to investigate the dependence of tribocorrosion on time. As rubbing proceeded, the mass loss rate of 304SS decreased, and the dominant wear mechanism changed from abrasion to delamination. In addition, during tribocorrosion, friction-induced α′-martensite would be transformed at room temperature. The volume fraction of transformed martensite was determined by test time, which played a dual role in accelerating corrosion and reducing wear. Additionally, the synergistic effect between corrosion and wear was analyzed; the main causes of 304SS degradation during tribocorrosion were pure mechanical wear and corrosion accelerated wear.     

Corrosion and tribocorrosion study of 316L steel,Ti–6Al–4V and Ti–10Zr–10Nb–5Ta

ABSTRACT

In this paper, corrosion and tribocorrosion tests have been conducted on three biomaterials: Ti–6Al–4V and 316L steel that are well-known commercial biomaterials and Ti–10Zr–10Nb–5Ta, a new biomaterial elaborated in a levitation-melting furnace. Tests have been conducted in five different electrolytes: NaCl (9g/l), Ringer’s solution, phosphate buffered saline solution (PBS) with and without an addition of bovine serum albumin (BSA). Two amounts of BSA were used: 1 and 5?g/l. In NaCl solution, Ringer’s solution and PBS solution, Ti–10Zr–10Nb–5Ta presents the best corrosion resistance. Conversely, in the presence of proteins, 316L steel shows better resistance to corrosion in comparison with Ti–10Zr–10Nb–5Ta and Ti–6Al–4V. During tribocorrosion tests, the surfaces have been submitted to friction against an alumina ball at open circuit potential (OCP). Measurement of wear rate at the end of the tests indicates clearly that 316L steel shows better resistance to material removal in comparison with Ti–10Zr–10Nb–5Ta and Ti–6Al–4V.     

Wear of CoCrMo alloys used in metal-on-metal hip joints: A tribocorrosion appraisal

A good biocompatibility, excellent mechanical properties and high corrosion resistance characterize CoCrMo alloys. Therefore they are widely used for artificial joints in biomedical implants. However, the degradation of the implants during service life leads to the release into the body of toxic ions and wear particles. This continuous degradation is of concern for long-term stability of the implants. Published literature has highlighted the relevance of lubrication as well as metallurgical and contact mechanical factors on the degradation of CoCrMo implant alloys. Recent experimental investigations have proposed tribocorrosion, i.e., the interplay of mechanical wear and corrosion by the body fluids, as one of the crucial degradation mechanism of implants. Tribocorrosion is sub-discipline of tribology and corrosion that recently made significant progresses in mechanistic understanding and modelling. The present work aims at evaluating published results on the degradation of CoCrMo alloys using existing tribocorrosion concepts. Results show that wear accelerated corrosion due to mechanical removal of the passive film during sliding is a major contribution to the overall degradation. Further, a transition from low (10^?6 N/mm³ m) to high (10^?4 N/mm³ m) wear coefficients was found at a threshold electrode potential close to 0.2 V_SHE These findings clearly show that electrochemical phenomena play a key role on the tribological behaviour of biomedical CoCrMo alloy implants.     

Triboelectrochemical behaviour of a Si3N4–TiN ceramic composite and a titanium alloy commonly used in biomedical applications

In this paper the corrosion and tribocorrosion behaviour of a traditional metallic biomaterial (Ti6Al4V) and a Si₃N₄/TiN (SN/TiN) ceramic composite are studied and compared during exposures to 1% NaCl and 1% NaCl + 1% lactic acid solutions.Electrochemical impedance spectroscopy (EIS) data collected on Ti6Al4V in both neutral and acidic solution have been interpreted on the basis of a double layer surface oxide film, which is completely removed from the wear track during the sliding tests. Under these conditions, the impedance of the depassivated region dominates the overall electrode impedance.Previous EIS tests performed on SN/TiN evidence that even this material exposed to neutral solution is covered by a double layer film, while a porous monolayer film forms in acid solution. Under pure corrosion conditions, SN/TiN exhibits corrosion rates which are quite comparable to those measured on Ti6Al4V. During tribocorrosion tests the EIS response of the ceramic material does not change much. Its corrosion rates are two orders of magnitude lower than those measured on Ti6Al4V.Profilometer analysis shows that on both materials most of overall tribocorrosion damage is due to mechanical wear.The tests suggest that SN/TiN is a promising biomaterials for applications where sliding conditions occur.