Tribological properties of Mo–S–I nanowires as additive in oil

A new nanowire-like material with the chemical formula Mo₆S_4.5I_4.5 was studied as additive in a synthetic base oil, a polyalphaolefin (PAO). This material presents interesting friction reducing properties, with friction coefficients reaching a value of 0.04 in boundary lubrication. Transmission and scanning electron microscopy, X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy were used to characterise nanowires before and after friction. The combination of these techniques gave evidence of MoS₂ formation in the contact area during friction tests. This structural evolution of nanowires explains their good friction reducing properties.     

Tribological performances of ZDDP and ashless triphenyl phosphorothionate (TPPT) as lubricant additives on Ti–N and Ti–Al–N coated steel surfaces

Abstract

In recent years, there has been much attention on the effects of lubricant additives on the friction and wear properties of surface coatings. However, little research has been conducted to investigate the influence of antiwear additives on the tribological performances of titanium nitride (Ti–N) and titanium aluminium nitride (Ti–Al–N) coatings. It has been reported that introducing aluminium into Ti–N coatings enhanced their oxidation resistance. In this study utilising a pin on cylinder tribometer, lubricants containing zinc dialkyl dithiophosphate (ZDDP) or a more environmentally friendly alternative, ashless triphenyl phosphorothionate (TPPT), were used. Experimental results revealed that ZDDP and TPPT helped to reduce wear on both coatings through the formation of a tribofilm, although it was also found that both additives increased the friction coefficient on both surfaces. Based on overall findings, this paper suggests the use of TPPT as a suitable ZDDP replacement for providing wear protection on Ti–N and Ti–Al–N coatings.     

Tribological study of novel S–N style 1,3,4-thiadiazole-2-thione derivatives in rapeseed oil

Two non-phosphorus and ashless 1,3,4-thiadiazole-2-thione derivatives, 5-dodecyldithio-3-phenly-1,3,4-thiadiazole-2-thione (DPTT) and 5-cetyldithio-3-phenyl-1,3,4-thiadiazole-2-thione (DHTT), were synthesized and their tribological behaviors as additives in rapeseed oil (RSO) were evaluated using a four-ball friction and wear tester. Their thermal stabilities and anticorrosive properties were investigated. The results indicate that the additives possess good thermal stabilities, corrosion inhibiting abilities and excellent load-carrying capacities. Moreover, they both have good anti-wear and friction-reducing property at relatively low concentration and under all test loads. The worn surfaces of the steel balls were observed using a scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). It is supposed that the synthetic additives adsorb and react with the steel surfaces during the rubbing process and generate a surface protective film composed of sulfate, sulfide, iron oxide and organic nitrogen-containing compounds, which accounts for the better tribological behaviors of the base stock containing the synthetic additives as compared with the base stock alone.     

Tribological behavior of fullerene–styrene sulfonic acid copolymer as water-based lubricant additive

A novel fullerene–styrene sulfonic acid copolymer was synthesized. The tribological properties of base stock (2 wt.% triethanolamine aqueous solution) containing the fullerene copolymer were measured using a four-ball tribotester. Experiments indicated that the anti-wear performance and load-carrying capacity of the base stock were raised and its friction coefficient was decreased. Then, the surface of worn scar was investigated by using electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS). Finally, its lubrication mechanism was deduced preliminarily.     

Tribological properties of Mg/Al–CO3 layered double hydroxide as additive in base oil

Abstract

The tribological performance of Mg/Al–CO₃–layered double hydroxide (LDHs) nanoparticles in base oil was studied as a sole additive and in combination with zinc dialkyldithiophosphate (ZDDP) at 100°C. Results show that LDHs could improve antifriction and antiwear properties of base oil. The blend with LDHs alone shows better antifriction properties than that of the mixture of LDHs and ZDDP, but the addition of ZDDP helps to stabilise the friction coefficient. Surface analyses have been performed to study the morphology, nanoparticle distribution and chemical species in the tribofilm. The results show that tribofilms contain Mg, Al, C, O, Zn, P and S, and the structure of Mg/Al–CO₃–LDHs changes under shearing stress and this process can help reduce friction coefficient. Thus, LDHs could be chemically incorporated into tribofilm to reduce the polyphosphate chain length originated from ZDDP decomposition resulting in a medium chain polyphosphate, which provides very good wear protection.     

Friction and wear of aluminium–steel contacts lubricated with ordered fluids-neutral and ionic liquid crystals as oil additives

Friction and wear of ASTM B211 aluminium–AISI 52100 steel contacts have been determined using pin-on-disk tests under variable conditions of normal applied load, sliding speed and temperature, in the presence of a lubricating base oil modified with a 1 wt.% proportion of three different liquid crystalline additives.The tribological behavior of the ionic liquid crystal n-dodecylammonium chloride (LC3) has been compared with that of two neutral liquid crystals: a non-polar species, 4,4′-dibutylazobenzene (LC1) which had previously shown its ability to lower friction and wear of metallic pairs as compared to the base oil, and a cholesterol derivative, cholesteryl linoleate (LC2).At low temperature and low sliding speed values, the friction coefficients obtained for LC1 are lower than those of LC3. As the severity of the contact conditions increases, this tendency reverses and the ionic species LC2 gives rise to lower friction values than LC1.Wear volume losses under increasing normal loads, between 2.45 and 5.89 N, are always lower in the presence of the ionic additive LC3.Lubrication and wear mechanisms are discussed from optical microscopy and SEM observation of the wear scars and wear debris morphology.     

Tribological Properties of Twin Electron-Beam Evaporated Cr–N and Al–Cr–N Coatings Under Laboratory Sliding and Drill Experiments

The tribological behavior of substoichiometric Cr–N and Al–Cr–N coatings prepared by twin electron-beam evaporation at 450 °C was studied. Al–Cr–N coatings with Al to Cr ratios in the range of 1–8 (and nitrogen concentrations of ~45 at.%) were synthesized and compared to Cr–N reference samples. The focus of this work is on Al–Cr–N (Al ≥ 30 at.%) coatings with the aim of (a) replacing Cr with Al due to environmental concerns and (b) achieving improved mechanical properties, and tribological performance. The composition, structure, mechanical and tribological properties of the coatings were determined using X-ray photoelectron spectroscopy, X-ray diffraction, and scanning electron microscopy in combination with nanoindentation measurements, laboratory controlled ball-on-disk sliding experiments, and wet and dry drilling experiments. It was found that all Al–Cr–N coatings exhibit higher hardness values compared to Cr–N coatings. Al–Cr–N coatings with Al contents and Al/Cr ratios of ≤38 at.% and ≤1.7, respectively, showed better performance than the rest of the coatings during both drilling and laboratory tribological experiments.     

Tribological Performance of Halogen-Free Ionic Liquids in Steel–Steel and DLC–DLC Contacts

The tribological performance of halogen-free ionic liquids at steel–steel and diamond-like carbon (DLC)–DLC contacts was investigated. Hydrogenated amorphous carbon (a-C:H) and tetrahedral amorphous carbon (ta-C) were used as test specimens. Friction tests were carried out on steel–steel, a-C:H–a-C:H, and ta-C–ta-C contacts by using a reciprocating cylinder-on-disk tribotester lubricated with two different types of halogen-free ionic liquids: 1-ethyl-3-methylimidazolium dicyanamide ([BMIM][DCN]) and 1-butyl-3-methylimidazolium tricyanomethanide ([BMIM][TCC]). From the results of friction tests, the ta-C–ta-C tribopair lubricated with [BMIM][DCN] or [BMIM][TCC] exhibited an ultralow friction coefficient of 0.018–0.03. On the other hand, ultralow friction was not observed at the steel–steel and a-C:H–a-C:H contacts. Measurements obtained with a laser scanning microscope and an atomic force microscope (AFM) showed that a chemical reaction film, derived from the ionic liquid lubricant used, was formed on the steel surfaces. However, this chemical reaction film was not observed on either of the DLC surfaces. The AFM results showed that there were high-viscosity products on the ta-C surfaces, that the wear tracks on the ta-C surfaces exhibited low frictional properties, and that the ta-C surfaces were extremely smooth after the friction tests. Based on these results, it was concluded that an ionic liquid–derived adsorbed film formed on the ta-C surface and resulted in the ultralow friction when lubricated with a halogen-free ionic liquid.     

Numerical calculation of temperature in the wheel–rail flange contact and implications for lubricant choice

The realization of movement by railway vehicles creates a problem that is connected to the wear process for elements of a tribological wheel–rail system. Wheel–rail wear is a complex phenomenon that depends on many factors. One of the main wear zones is the contact area between a wheel flange and a rail gauge. As is well known, wear in this contact zone occurs when a railway vehicle moves on curved parts of track, realizes tractive, braking efforts or moves in a high-speed mode. In this case, the solution of this kind of wear problem can be found by means of lubricant implementation. The choice of a lubricant requires information about contact characteristics at the moment of a vehicle's movement. This paper focuses on the modeling of the temperature process in the contact between a wheel flange and a rail gauge. Examples of temperature calculation with some experimental data as input for this computation are presented. The obtained values of the temperature allow for making the correct choice of lubricant type.     

Using Methods of Analysis of Optical Images of Friction Surfaces of Ti–Al–N Based Coatings for Assessing Accumulation of Damage and Diagnostics of Failure in Tribological Tests

Russian Journal of Nondestructive Testing - The processes of damage accumulation and failure in thin ceramic coatings based on the Ti–Al–N system deposited on ductile steel and brittle...     

Arc Evaporation of Ti–Al–Ta–N Coatings: The Effect of Bias Voltage and Ta on High-temperature Tribological Properties

Recently, titanium aluminium tantalum nitride (Ti–Al–Ta–N) coatings have been shown to exhibit beneficial properties for cutting applications. However, the reason for the improved behaviour of these coatings in comparison to unalloyed Ti–Al–N is not yet clear. Here, we report on the tribological mechanisms present in the temperature range between 25 and 900 °C for this coating system, and in particular on the effect of the bias voltage during deposition on the tribological response. Based on these results, we provide an explanation for the improved performance of Ta-alloyed coatings. An industrial-scale cathodic arc evaporation facility was used to deposit the coatings from powder metallurgically produced Ti₄₀Al₆₀ and Ti₃₈Al₅₇Ta₅ targets at bias voltages ranging from −40 to −160 V. X-ray diffraction experiments displayed a change with increasing bias voltage from a dual-phase structure containing cubic and hexagonal phases to a single-phase cubic structure. Investigations of the wear behaviour at various temperatures showed different controlling effects in the respective temperature ranges. The results of dry sliding tests at room temperature were independent of bias voltage and Ta-alloying, where the atmosphere, i.e. moisture and oxygen, were the most important parameters during the test. At 500 °C, bias and droplet-generated surface roughness were identified to determine the tribological behaviour. At 700 and 900 °C, wear depended on the coating’s resistance to oxidation, which was also influenced by the bias voltage. In conclusion, Ta-alloyed coatings show a significantly higher resistance to oxidation than unalloyed Ti–Al–N which could be an important reason for the improved performance in cutting operations.     

Tribological Characteristics of Calophyllum inophyllum–Based TMP (Trimethylolpropane) Ester as Energy-Saving and Biodegradable Lubricant

The purpose of this research is an experimental study of Calophyllum inophyllum (CI)-based trymethylolpropane (TMP) ester as an energy-saving and biodegradable lubricant and compare it with commercial lubricant and paraffin mineral oil using a four-ball tribometer. CI-based TMP ester is a renewable lubricant that is nonedible, biodegradable, and nontoxic and has net zero greenhouse gases. The TMP ester was produced from CI oil, which has high lubricity properties such as higher density, higher viscosity at both 40°C and 100°C and higher viscosity index (VI). Experiments were conducted during 3,600 s with constant load of 40 kg and constant sliding speed of 1,200 rpm at temperatures of 50, 60, 70, 80, 90, and 100°C for all three types of lubricant. The results show that CI TMP ester had the lowest coefficient of friction (COF) as well as lower consumption of energy at all test temperatures, but the worn surface roughness average (R_a) and wear scar diameter were higher compared to paraffin mineral oil and commercial lubricant. Before 80°C, CI TMP ester actually has a higher flash temperature parameter (FTP) than paraffin mineral oil and as the temperature increases, the FTP of TMP ester decreases. The worn surfaces of the stationary balls were analyzed by scanning electron microscopy (SEM) and results show that CI TMP ester has the highest wear compared to paraffin mineral oil and lowest wear compared to commercial lubricant. However, CI TMP ester is environmentally desired, competitive to commercial lubricant, and its use should be encouraged.     

Mapping erosion–corrosion of carbon steel in oil–water solutions: Effects of velocity and applied potential

In this study, the erosion–corrosion performance of carbon steel was investigated in crude oil, reservoir water, and a mixture of both solutions at a range of applied potentials, velocities and impact angle. The application of such work is to upstream and downstream oilfield conditions, where the proportions of hydrocarbon and water may vary during the extraction process over time. Following exposure of the carbon steel in the crude oil, the extent of erosion was greater than that of corrosion, whilst in the reservoir water, the erosion and corrosion contributions were similar. Regimes of erosion–corrosion were proposed based on the variation in erosion behaviour at various impact angles and applied potentials in the environments studied. Mechanistic changes were identified on erosion–corrosion maps as a function of velocity and applied potential at various impact angles, indicating important transitions in erosion–corrosion processes in the oil/water environments.     

Comparative study of the tribological behavior of self-lubricating W–S–C and Mo–Se–C sputtered coatings

Transition metal dichalcogenides (TMD) have been one of the best alternatives as low friction coatings for tribological applications, particularly in dry and vacuum environments. However, besides their deficient behavior in humid containing atmospheres, their extensive application has also been restricted due to their low load-bearing capacity. In order to overcome these problems, recently the alloying with C has been tried with the expectation of simultaneously improving the coatings hardness and reaching sliding contacting phases more convenient for achieving low friction in humid environments.The practical application of this concept was extensively studied with the W–S–C system, with the C addition being achieved either by reactive or co-sputtering processes. The best tribological results were obtained by co-sputtering from a C target embedded with an increasing number of WS₂ pellets. Excellent results were reached from the more than one order of magnitude increase in the coatings hardness up to friction coefficients which are close to those of the references of self-lubricating coatings: TMD for dry or vacuum atmospheres or C-based coatings for terrestrial sliding conditions.Following the good results achieved with W–S–C system, other TMDs systems have been envisaged to be studied. The main focus was placed on the Mo–Se–C system.In this paper, the general comparison between W–S–C and Mo–Se–C coatings is presented. The main effort is pointed on the tribological behavior of both systems when tested by pin-on-disk against steel counterpart balls under different testing conditions: applied normal loads, temperatures and relative humidity of the atmospheres. Both coatings were deposited by co-sputtering from a C target with a varying number of TMD pellets which could lead to C contents in the films in the range from 30  up to 70 at.%. A Ti interlayer was interposed between the films and the substrates for improving the adhesion.Typically, W–S–C films are harder than Mo–Se–C films. From the tribological point of view, W–S–C films are more thermally stable than Mo–Se–C films although the friction coefficients of these last ones are lower when tested in humid containing atmospheres.     

An experimental study of process variables in turning operations of Ti–6Al–4V and Cr–Co spherical prostheses

Ti–6Al–4V and Cr–Co alloys are extensively used in manufacturing prostheses due to their biocompatibility, high strength-to-weight ratio and high resistance to corrosion and wear. However, machining operations involving Ti–6Al–4V and Cr–Co alloys face a series of difficulties related to their low machinability which complicate the process of controlling the quality levels required in these parts. The main objective of this paper is to study the influence of cutting parameters, machine tool control accuracy and metrology procedures on surface roughness parameters and form errors in contouring operations of Ti–6Al–4V and Cr–Co workpieces. The machining performance of the two biocompatible materials is compared, focusing the study on part quality at low feed per revolution and the stochastic nature of plastic deformations at this regime. The results showed a better surface roughness control for Ti–6Al–4V, whereas for Cr–Co alloys, the performance presents high variability. In the case of form errors (sphericity), contouring errors and metrology procedures are important factors to be considered for quality assurance. In addition, the study analyses the correlation of the machining performance with different sensor signals acquired from a low cost non-intrusive multi-sensor, showing a high correlation of signals from acoustic emission sensors and accelerometers in the machining of spherical features on Ti–6Al–4V parts. The findings of this research work can be taken into account when designing prostheses components and planning their manufacturing processes.     

Design of a Conductance and Capacitance Combination Sensor for water holdup measurement in oil–water two-phase flow

Oil–water two-phase flow widely exists in the process of petroleum industry. The liquid holdup measurement in horizontal pipeline is very important and difficult. In this work, a Conductance and Capacitance Combination Sensor (CCCS) system with four conductance rings and two concave capacitance plates is designed and validated for its measurement performance of in situ water holdup through dynamic experiments. A set of fast electronic switches controls the conductance rings and the capacitance plates alternatively set up each own sensing field in the same sensing volume. This configuration ensures the water holdup estimation in the range from 0% to 100% regardless of flow direction. A set of quick closing valves was used to acquire the in situ holdup for the on-line calibration of the CCCS system. The theoretical correlations of conductance sensor and capacitance sensor were established to make the real-time measurement convenient. A real-time measurement method by CCCS system is provided based on the fusion of the conductance and the capacitance measurement without flow pattern recognition. This method delivers an average error of 1.06% for the CCCS system measuring the water holdup of oil–water two-phase flow, with a standard deviation of 0.038 and a relative error less than ±5%.     

Corrosion-Wear Resistance and Interfacial Morphologies of Novel Fe–Cr–B Cast Steels in Molten Aluminum

In order to improve the corrosion–wear resistance properties of steels in molten aluminum, novel Fe–Cr–B cast steels with different boron concentrations were prepared. The steels were investigated at 750 °C for 0.5 h using a ring-block corrosion–wear test, and the interfacial morphologies were examined. Results showed that the corrosion–wear resistance of the Fe–Cr–B cast steel was three times that of H13, and benefited greatly from the effects of the primary Cr-rich Fe₂B, which bore the main load during the corrosion–wear test. The corrosion–wear behavior of the coarse primary Cr-rich Fe₂B in molten aluminum was clearly different from that in static molten aluminum.     

Precise volume fraction prediction in oil–water–gas multiphase flows by means of gamma-ray attenuation and artificial neural networks using one detector

Artificial neural network (ANN) is an appropriate method used to handle the modeling, prediction and classification problems. In this study, based on nuclear technique in annular multiphase regime using only one detector and a dual energy gamma-ray source, a proposed ANN architecture is used to predict the oil, water and air percentage, precisely. A multi-layer perceptron (MLP) neural network is used to develop the ANN model in MATLAB 7.0.4 software. In this work, number of detectors and ANN input features were reduced to one and two, respectively. The input parameters of ANN are first and second full energy peaks of the detector output signal, and the outputs are oil and water percentage. The obtained results show that the proposed ANN model has achieved good agreement with the simulation data with a negligible error between the estimated and simulated values. Defined MAE% error was obtained less than 1%.     

Effect of as-ground surface and the BALINIT® C and Nb–S coatings on contact fatigue damage in gears

The influence of as-ground surface and the BALINIT^® C and Nb–S coatings on contact fatigue damage have been investigated using testing of case-carburised S156 steel helical gears. The micro-surface features on the as-ground gear flank tend to initiate micro-pitting. In BALINIT^® C coated gears, the surface irregularities are removed by polishing effect resulting in small scale initiation of micro-pitting at the interface between polished and unpolished regions. In Nb–S coated gears, the coating tends to penetrate and fill-up the surface micro-valleys and hence showed only scattered micro-pitting. The Nb–S coated gears did not produce any tooth profile loss whilst the BALINIT^® C coated gears produced profile loss. However, both BALINIT^® C and Nb–S coated gears show enhanced contact fatigue performance.