Tribochemical Effects Research Articles

Influence of Interfacial Tribo-Chemical and Mechanical Effect on Tribological Behaviors of TiN Film in Different Environments

A series of experiments has been conducted to investigate the tribological properties of a TiN film sliding against GCr15 steel balls in ambient air, low vacuum and high vacuum environments. Various friction loads and sliding velocities were also applied. The TiN film displays a steady-state friction stage after the running-in stage in all the above environments, while the durations of running-in stages are different. The steady-state friction coefficients of the TiN film were around 0.56 in ambient air and 0.3 in the high vacuum environment (1 × 10−5 mbar). In the low vacuum (1 × 10−2 mbar) environment, a low friction coefficient (around 0.19) was attained for all the friction tests on TiN film, irrespective of the applied load and sliding velocity. In the meantime, it was noticed that the applied loads and the sliding velocities would change the duration of the running-in stage before reaching the low friction coefficient. It is revealed by the analysis of wear tracks that the metal oxides induced by the tribo-chemical effect at the friction interface play an important role in affecting the tribological behaviors of the TiN films in different environments. The Raman results show that the main component of the metal oxides is hematite (α-Fe2O3), and the amount of iron oxide is related to the friction environment. The composition and quantity of iron oxides produced by the interfacial tribo-chemical effect affect the tribological behavior. The results also show that the mechanical wear process at the friction interface displays a polishing effect, which would reduce the surface roughness. The mechanical wear performance varies under different loads and velocities. The tribological tests results indicate that the interfacial tribo-chemical effect and mechanical wear process should be considered together rather than individually to interpret the tribological behaviors of TiN films in different environments.

Wear behavior of multilayer coated carbide tools in finish dry hard turning

Abstract The aim of this study is to explore wear behaviors of carbide tools with a multilayer TiCN + Al2O3 + TiN coating on AISI-4340 and AISI-52100 hardened steel substrates generated by the medium temperature chemical vapor deposition (MTCVD) method in finish dry hard turning. Microscopic and microstructural wear aspects of multilayer-coated carbide tips were quantified at three cutting speeds using a constant feed rate of 0.027 mm × rev−1 and a constant cutting depth of 0.2 mm. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to investigate worn tool surfaces, wear products and wear mechanisms. Wear mechanisms observed involved abrasion, adhesion, plastic flow, material transfer and tribochemical effects depending on mechanical and thermal conditions generated on the wear zones. Transfer layer formation with different morphologies was distinguished to occur at the rake-chip interface.

Material removal model of chemical mechanical polishing for fused silica using soft nanoparticles

Fiber arrays are used to connect arrayed waveguide chips. The end-faces of fiber array components are multi-materials non-uniform surfaces. Their low polishing quality has become a bottleneck that restricts coupling performance of integrated photo-electronic devices. The chemical mechanical polishing (CMP) is normally used to improve the polishing quality of the end-faces of fiber array components. It is very important to optimize process parameters by researching the mechanical behavior of nanoparticles and material microstructure evolution on the CMP interfaces. Based on the elastic and hyper-elastic contact of the soft polishing nanoparticles with fused silica and polishing pad, respectively, the material removal mechanism at molecular scale of polishing process for fused silica using nanoparticles is investigated, and the material removal rate model is also derived by using Arrhenius theory and molecule vibration theory. Theoretical and experimental results show that the material is mainly removed by the interfacial tribo-chemical effect between polishing nanoparticles and fused silica during CMP process. The penetration depth of a single nanoparticle inside the fused silica is at molecular scale, and the superficial molecules of fused silica are removed by chemical reactions because of enough energy obtained. The material removal rate of fused silica during CMP process is determined by the polishing pressure, the chemical reagents and its concentration, and the relative movement speed between the fused silica workpiece and the polishing pad.

Comparison of Alcohol and Fatty Acid Adsorption on Hydrogenated DLC Coatings Studied by AFM and Tribological Tests

Adsorption on hydrogenated diamond-like carbon (DLC) coatings with respect to boundary lubrication has been studied only very rarely, even though such adsorption has proved to be one of the main boundary-lubricating mechanisms for metal contacts. For this reason, we used atomic force microscopy (AFM) and tribotests to study the ability of hexadecanol and hexadecanoic acid to adsorb onto DLC and affect the tribological properties of DLC coatings, where steel was used as a reference. We have shown that alcohols and fatty acids can adsorb onto the DLC under static conditions. However, under dynamic tribocontact conditions, although alcohol and fatty acid molecules help to decrease the wear of the coatings, they are inefficient in reducing the friction. In all the experiments the fatty acid proved to have superior adsorption abilities compared to the corresponding alcohol. Based on our results and the existing literature, tentative adsorption mechanisms that include an environmental species effect, a temperature effect and a tribochemical effect are discussed for DLC surfaces.

Adsorption mechanisms for fatty acids on DLC and steel studied by AFM and tribological experiments

Fatty acids are known to affect the friction and wear of steel contacts via adsorption onto the surface, which is one of the fundamental boundary-lubrication mechanisms. The understanding of the lubrication mechanisms of polar molecules on diamond-like carbon (DLC) is, however, still insufficient. In this work we aimed to find out whether such molecules have a similar effect on DLC coatings as they do on steel. The adsorption of hexadecanoic acid in various concentrations (2–20mmol/l) on DLC was studied under static conditions using an atomic force microscope (AFM). The amount of surface coverage of the adsorbed fatty-acid molecules was analysed. In addition, tribological tests were performed to correlate the wear and friction behaviours in tribological contacts with the adsorption of molecules on the surface under static conditions. A good correlation between the AFM results and the tribological behaviour was observed. We confirmed that fatty acids can adsorb onto the DLC surfaces and are, therefore, potential boundary-lubrication agents for DLC coatings. The adsorption of the fatty acid onto the DLC surfaces reduces the wear of the coatings, but it is less effective in reducing the friction. Tentative adsorption mechanisms that include an environmental species effect, a temperature effect and a tribochemical effect are proposed for DLC and steel surfaces based on our results and few potential mechanisms found in literature.

Tool Wear Mechanisms during Machining of Alloy 625

Nickel-base superalloys like Alloy 625 are widely used in power generation applications due to their unique properties especially at elevated temperatures. During the related component manufacturing for gas turbines up to 50% of the material has to be removed by metal cutting operations like milling, turning or drilling. As a result of high strength and toughness the machinability of Alloy 625 is generally poor and only low cutting speeds can be used. High-speed cutting of Alloy 625 on the other hand gets more important in industry to reduce manufacturing times and thus production costs. The cutting speed represents one of the most important factors that have influences on the tool life. The aim of this study is the analyses of wear mechanisms occurring during machining of Alloy 625. Orthogonal cutting experiments have been performed and different process parameters have been varied in a wide range. New and worn tools have been investigated by stereo microscopy, optical microscopy and scanning electron microscopy. Energy-dispersive X-ray analyses were used for the investigation of chemical compositions of the tool's surface as well as the nature of reaction products formed during the cutting process. Wear mechanisms observed in the machining experiments included abrasion, fracture and tribochemical effects. Specific wear features appeared depending on the mechanical and thermal conditions generated in the wear zones.

Categorization system of nanofillers to polymer composites

The paper deals with a systematic categorization of nanofillers in terms of their effect arising upon introduction into polymer composites of tribological applications. The authors study the nature of this effect and the tribological behavior of different types of nanofillers acting in composites and exhibiting either a tribochemical effect or a discrete surface one. Nanofillers having an indirect influence on friction and intercalation compounds are also studied.

Wear development on wiper Al 2O 3–TiC mixed ceramic tools in hard machining of high strength steel

This paper explores the wear mechanisms occurring for the mixed ceramic inserts against 60 HRC alloy steel (equivalent to AISI 5140 or DIN 41Cr4) specimens in dry and hard finish turning operations. Several machining wear tests were performed under varying feed rate, constant cutting speed of 100 m/min and small depth of cut of 0.2 mm. Light optical microscopy (LOM), scanning electron microscopy (SEM) and back-scattering electron (BSE) technique were employed to observe morphological features of worn surfaces produced by various wear mechanisms. In addition, the elemental compositions of wear products were evaluated by energy-dispersive X-ray (EDX) micro-analysis, called sometimes energy-dispersive X-ray spectroscopy (EDS). As a result, both microscopic and microstructural aspects of ceramic tool wear were considered. In general, wear mechanisms identified in the machining tests involve abrasion, fracture, plastic flow and transferred layers, BUE and tribochemical effects. Specific wear symptoms appeared depending on the mechanical and thermal conditions generated in the wear zones. In particular, two types of material transfer with different morphologies occurring at the rake–chip interface are distinguished.

High temperature fretting wear of a Ti alloy/CuNiIn contact

Fretting wear is a surface degradation process invariably observed when two contacting bodies are subjected to small amplitude oscillatory movements. In the blade/disk contact of aero-engines especially, movements induced by the engine regime changes may lead to critical wear. In order to limit friction and protect components, motorists usually use a thick and soft CuNiIn layer (150 µm). This system is subjected to high contact pressure (up to 600 MPa) and high temperatures (up to 500 °C). This paper focuses on the identification of the degradation mechanisms of such a system. An experimental layout was designed to perform fretting wear tests up to 500 °C. A punch (commercial Ti17) on plane (Ti6242 coated with CuNiIn) geometry was chosen and fretting tests were performed at several temperatures (20 °C, 250 °C, 350 °C and 450 °C). Surface damage evolution was followed by 3D profilometry and several analyses (SEM, EDS, µ-hardness) were conducted on the surface and on cross-sections. Based on the results, specific degradation mechanisms were identified for this Ti17/CuNiIn contact at high temperatures, suggesting that the tribochemical effects should be considered in the fretting wear models.

Wear phenomenon in the hard steel machining using ceramic tools

The principle aim of this investigation is to recognize the wear phenomenon of the mixed ceramic tips against 60 HRC steel specimens in dry and hard turning operations. For this purpose both microscopic and microstructural aspects of ceramic tool wear were taken into consideration. Investigations were performed under varying feed rate, constant cutting speed of 100 m/min and small depth of cut of 0.2 mm to perform finishing cuts. Light optical microscopy (LOM), scanning electron microscopy (SEM), BSE technique and X-ray diffraction analysis (XRM) were applied for observations of worn tool surfaces, wear products and the distinction of wear mechanisms occurring. In general, wear mechanisms observed in the machining tests involve abrasion, fracture, plastic flow, material transfer and tribochemical effects which appear depending on the mechanical and thermal conditions generated on the wear zones. In particular, two types of transfer layer formation with different morphologies occurring at the rake-chip interface are distinguished.

Tribochemical Effects of MoSi2 Powder in Ball Milling

The tribochemical effects of MoSi2 powder in the ball milling process have been studied by X-ray diffraction (XRD) and QM-4H milling machine. It has been found that the intensity of diffraction peak of MoSi2 powder is continuously decreased and the width increased with the increase of milling time. Specifically, the crystallite size decreased largely in the early stage of milling. Contrary to the above, the microstrain and the effective temperature factor increased considerably. After ninety hours of milling, the crystallite size had little changes. The relations among the tribochemical effect factors are as follows: the microstrain and the effective temperature factor increase with the decrease of the crystallite size. The microstrain increases with the increase of the effective temperature factor.

Mechanisms of friction in diamondlike nanocomposite coatings

Diamondlike nanocomposite (DLN) coatings (C:H:Si:O) processed from siloxane precursors by plasma enhanced chemical vapor deposition are well known for their low friction and wear behaviors. In the current study, we have investigated the fundamental mechanisms of friction and interfacial shear strength in DLN coatings and the roles of contact stress and environment on their tribological behavior. Friction and wear measurements were performed from 0.25to0.6GPa contact pressures in three environments: dry (<1% RH) nitrogen, dry (<1% RH) air, and humid (50% RH) air, with precise control of dew point and oxygen content. At 0.3GPa contact stress, the coefficient of friction (COF) in dry nitrogen was extremely low, ∼0.02, whereas in humid air it increased to ∼0.2, with minimal amount of wear in both environments. The coatings also exhibited non-Amontonian friction behavior, with COF decreasing with an increase in Hertzian contact stress. The main mechanism responsible for low friction and wear under varying contact stresses and environments is governed by the interfacial sliding between the DLN coating and the friction-induced transfer film adhered to the ball counterface. This interfacial shear strength, computed from COF-inverse Hertzian contact stress plots, was found to be 9MPa in dry nitrogen and 78MPa in humid air. Time-of-flight secondary ion mass spectroscopy analysis of the interfaces (wear tracks and transfer films) was used to explain the tribochemical effects in both environments. The transfer films generated in humid air were found to be enriched with SiO2 containing fragments, whereas those formed in dry nitrogen had hydrogenated and long range ordered carbons with practically no SiO2 fragments, ultimately resulting in much lower interfacial shear strength and COF.

Tribochemical effects on the friction and wear behaviors of a-C:H and a-C films in different environment

Friction and wear behaviors of hydrogenated amorphous carbon (a-C:H) and hydrogen-free amorphous carbon (a-C) films sliding against Si 3N 4 balls were investigated in different testing environments. The result showed that two films with extreme chemical disparity (one hydrogenated, and the other hydrogen free) showed distinct different friction and wear behaviors, and the friction and wear behaviors of the both films were strongly dependent on the environment. For a-C:H films, much low friction coefficient and wear rate were obtain in dry N 2. In the water and/or oxygen containing environments, the friction coefficient and wear rate of a-C:H films were obviously increased. On the contrary, a-C films only provided low friction coefficient and wear rate in the presence of water and/or oxygen in the test chamber. In dry N 2, the highest friction coefficient and wear rate were observed for a-C films. By investigating the worn surfaces of the films using XPS, it was proposed that the environment dependence of the friction and wear behaviors of the films was closely related with the friction-induced chemical interactions between the films and water and/or oxygen molecules. The specific roles of hydrogen, water and oxygen molecules and their tribochemical effects on the friction and wear mechanism of the films are discussed.

Tribochemical effects on the friction and wear behaviors of diamond-like carbon film under high relative humidity condition

Friction and wear behaviors of diamond-like carbon (DLC) film in humid N2 (RH-100%) sliding against different counterpart ball (Si3N4 ball, Al2O3 ball and steel ball) were investigated. It was found that the friction and wear behaviors of DLC film were dependent on the friction-induced tribochemical interactions in the presence of the DLC film, water molecules and counterpart balls. When sliding against Si3N4 ball, a tribochemical film that mainly consisted of silica gel was formed on the worn surface due to the oxidation and hydrolysis of the Si3N4 ball, and resulted in the lowest friction coefficient and wear rate of the DLC film. The degradation of the DLC film catalyzed by Al2O3 ball caused the highest wear rate of DLC film when sliding against Al2O3 ball, while the tribochemical reactions between DLC film and steel ball led to the highest friction coefficient when sliding against steel ball.

Tribochemical Effects on Tribological Properties of Self-Mated Zirconia Ceramic in HFC-134a Gas

Tribochemical effects on the tribological properties of self-mated zirconia ceramic in CF3CH2F (HFC-134a) were investigated using a ball-on-disk type environmental tribometer. The friction chamber of the tribometer was attached to a micro-spot X-ray Photoelectron Spectrometer (XPS) for ensuring that surface analysis be conducted without exposuring the frictional surfaces to air. It was found that HFC-134a gas was an effective lubricant for zirconia ceramic, especially at a pressure higher than 103 Pa. The products of tribochemical reactions between zirconia and HFC-134a molecules were detected. The amount and chemical state of the tribochemical products seemed to control the tribological behaviors. Thus, the role of tribochemical products on the tribological properties of zirconia in HFC-134a gas at 104 Pa was studied in detail under applied loads of 0.6–5.0 N and sliding speed of 0.04–0.35 m/s. It was found that severe tribochemical reactions occurred at low speeds and high loads. The formation of ZrF4 accelerated the chemical wear of zirconia, and raised the friction. Zirconia ceramic is suitable for use at moderate load and sliding speed under a reactive environment.

Tribochemical effect of impurities in zinc dialkyldithiophosphate in engine oil

AbstractThis study deals with the effects of alcohols and ketones, two substances usually found in commercial zinc dialkyldithio‐phosphate (ZDDP), on the tribological behaviour of ZDDP. Experimental results show that two alcohol and ketone compounds, namely 2‐ethylhexanol and methyl isopropyl ketone, respectively, have an influence on the lubricity, wear resistance, and friction‐reducing properties of ZDDP. 2‐Ethylhexanol can increase the extreme‐pressure properties of ZDDP (the load‐carrying capacity of a lubricating oil being enhanced from 710 to over 1100 N). At the same time, the alcohol can also improve the wear resistance of ZDDP. However, this alcohol is detrimental to the antifriction properties of ZDDP, the friction coefficient of a lubricating oil being increased from 0. 0919 to 0. 1010. The antioxidative ability of ZDDP is weakened to some extent. The presence of a ketone, with a carbonyl group, greatly decreases the load‐carrying capacity of ZDDP, which goes down from 710 N to 597. 8 N on the addition of 1. 5 wt. % methyl isopropyl ketone to ZDDP. The mechanisms of the influence of the alcohol and ketone on ZDDP are also investigated.

A tentative explanation for the tribochemical effects in fretting wear

In many fretting investigations, tribochemical reactions have been reported to critically determine the wear and friction behavior, however, different and contradictory assessments of the importance of mechanical and thermal effects on these reactions have been suggested. Since fretting is characterized by relatively slow sliding speeds, high temperatures are not generated over the entire nominal contact area. However, evidence for phase transformations, which are typical of high temperatures, have been observed many times in fretting experiments. In other words, there exists a discrepancy between the macro- and micro-scale observations. In our previous experimental and theoretical work, the tribochemical transformations of steel and ceramics were extensively investigated and the presence of very high flash contact temperatures under gross slip fretting was confirmed. In this paper we present a tentative explanation of the mechanism for the observed tribochemical changes under selected fretting conditions, which can also explain the discrepancy in the results from macro- and micro-scale studies. The proposed wear mechanism considers the tribochemical transformations at the asperity spot-to-spot contacts due to high flash temperatures, while the heat generation and dissipation at apparent contact area remain significantly lower. The observed overall wear transition occurs due to gradual accumulation of the transformed material, which in “closed” fretting contacts remains in great part within the contact.

Thermal analysis of nonisothermal oxidation parameters of zirconium powder

The possibility of applying methods of differential thermal analysis (DTA) and thermogravimetry (TG) to the study of nonisothermal oxidation of metals is demonstrated, with zirconium as an example. The zirconium powders studied were produced by the sodium-thermal and electrolytic methods as well as by the electrolytic method with further grinding in a ballmill in alcohol for different time intervals. It was found that zirconium oxidation covers several stages corresponding to the oxidation of different-sized zirconium particles, which is confirmed by the increase in the thermal effect for a fraction of small particles depending on time of grinding and by its decrease for a fraction of large ones. It is also found that grinding affects heat evaluation rate and initial oxidation temperature, which is explained by the occurrence of a tribochemical effect. In order to increase this effect, it is proposed to introduce a liquid passivating agent into the ground powders.

Tribochemical effects on CN x films

CN x thin coatings have been deposited by dc magnetron sputtering using a graphite target in nitrogen atmosphere under different experimental conditions. X-Ray photoelectron spectroscopy, electron-energy loss spectroscopy, nuclear magnetic resonance and Fourier-transformed infrared spectroscopy were used to elucidate the structural chemistry of each film. The tribological behavior has been investigated using a reciprocating pin-on-flat tribometer in a wide range of environmental conditions: ambient air, dry air and nitrogen. Tribochemical effects in relation to the nature of the surrounding atmosphere during friction tests are presented. Strong relationships between the N/C ratio, the nature of C–N bonds and the friction behavior are highlighted and discussed. An optimum in the friction and wear properties was found for a maximum in the CN/CC ratio for the studied set of CN x samples. The XPS/AES analysis of the sliding counterfaces support a destabilization of the CN x network under friction and build-up of a carbon rich tribolayer under steady-state.

Tribochemical effects in formation of polymer transfer film

Friction and wear tests of various polymers/stainless steel, PTFE/various metals and JS material (a multilayer composite)/stainless steel were carried out. The XPS spectra and atomic relative concentrations of elements on mating surfaces, the EPM spectra of element line distributions on frictional surfaces and the ESR spectra of radicals in polymer wear debris were determined. The test results indicated that polymer transfer films were formed on all friction surfaces. Meanwhile, extremely complex tribochemical reactions took place on the interfaces. The friction and wear properties of polymer were closely related to the adherent strength and covering extent of the transfer film on the counterface. The transfer film formation was influenced by polymer structure characteristics, tribochemical reactions and friction conditions.