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Water can alter the performance of modern gear lubricants by influencing the flank load carrying capacity of gears significantly. The purpose of this paper is to investigate the influence of water contaminations in different kinds of base oils on the micro-pitting and wear performance of case carburized gears.

Concerning micro-pitting and wear, tests, based mostly on the following standardized tests, are performed on a Forschungsstelle fuer zahnraeder und getriebebau (FZG)-back-to-back gear test rig: micro-pitting short test Graufleckenkurztest (GFKT) according to DGMK 575 (screening test), micro-pitting test Graufleckentest (GT) according to FVA 54/7 (load stage test and endurance test) and Slow-speed wear test according to DGMK 377. To investigate the effect of water on the gear load carrying capacity dependent on different types of base oils, two polyglycol oils (PG1 and PG2), a polyalphaolefin oil, a mineral oil and an ester oil E are used. Each of these oils are common wind turbine gear oils with a viscosity ISO VG-220. Additionally, a manual transmission fluid with a viscosity of society of automotive engineers (SAE) 75W-85 is tested.

Considering the micro-pitting and wear performance, a significant decrease caused by water contaminations could not be detected. Regarding pitting damages, a generally negative influence was observed. This influence was differently distinctive for different base oil types. Especially non-polar lubricants seem to be affected negatively. The documented damages of the tooth flanks confirm this observation. While typical pitting damages appeared in test runs with polar lubricants, the disruption in test runs with non-polar lubricants was more extensive. Based on the experimental investigations, a general model of the damaging mechanisms of water contaminations in lubricants was derived. It is split into three partitions: interaction lubricant–water (effect of water on the molecular structure of base oils and additives), chemical-material-technological (especially corrosive reactions) and tribological influence (effect of water droplets in the contact zone). It has to be considered that the additive package of lubricants affects the influence of water contaminations on the flank load carrying capacity distinctively. An influence of water on the micro-pitting and wear performance in other than the given lubricants cannot be excluded.

While former research work was focused more on the effects of water in mineral oils, investigations concerning different types of base oils as well as different types of damages were carried out within this research project.

The aim of this work is the study the tribological behaviour and tribocorrosion resistance of newly developed multilayer PVD coatings Cr/CrN and CrN/ZrCN applied on nitrided F1272 steel for gear applications.

Tribological characterization has been completed by several tribological tests performed under ball‐on‐disc configuration, extreme pressure tests to determine the maximum load before the films failure and rolling‐sliding tests under line‐contact conditions (35‐40 per cent of sliding). The response of the different coatings to sodium chloride aggressive environment has been simulated by accelerated tribocorrosion tests, combining simultaneously chemical and mechanical factors. The synergistic effect of wear on corrosion behaviour and vice versa, has been studied in order to compare the protective properties of the different PVD coatings developed.

Cr/CrN PVD coating improves wear in almost a 90 per cent compared to the nitrided substrate, presenting a similar behaviour to this one under extreme pressure conditions. CrN/ZrCN coating also improved substrate wear and especially good behaviour for this coating was observed under extreme pressure conditions. Cr/CrN coating strongly decreases micropitting and scuffing effect when it is tested under rolling‐sliding configuration. Under micro‐pitting conditions, coating protects the substrate and reduces the fatigue of uncoated discs. When adhesive wear (scuffing) is studied also Cr/CrN improves notable the nitrided steel performance. Under simultaneously corrosion‐wear conditions, Cr/CrN coating registered the lowest material loss because in this case only corrosion effect contributed to the coated surface degradation being the mechanical contribution inappreciable.

New multilayer coatings with improved wear performance and tribocorrosion resistance have been developed and comprehensively characterized. These coatings can be used in advanced gears for corrosive environmental conditions as well as with biodegradable lubricants.

The abrasive wear performance of fly ash filled aramid fibre reinforced phenolic based composites has been investigated on a rubber wheel abrasive wear tester (RWAT). The design of the experiment approach which uses Taguchi’s orthogonal arrays is adopted to objectively evaluate and prioritize five influencing factors that are taken as experimental variables. A predictive mathematical model for damage assessment in wear rate is developed and validated by a well designed set of experiments. The study reveals that sliding distance, external abrading particle size and fly ash content show greater influence on the specific wear rate of the composites. An investigation on worn surface morphology with a scanning electron microscope (SEM) has been carried out to understand the plausible wear mechanisms. The study thus carried out has revealed the decisive role of quartz particles and photovoltaic (PV) conditions in terms of their influence not only on the alterations of topographical attributes, but also surface ploughing, micro-pitting and sub-surface damage as the various modes of wear of these composites.

The purpose of this study is to investigate the use of micro-pits technology to the problem of tribological performance in a sliding motion.

Vegetable oil is a sustainable and economically viable alternative to both mineral and synthetic oils, offering significant savings in both the cost of research and manufacturing. To solve the depriving issue and boost lubrication film thickness, the micro-pits on the surface may function as reservoirs that provide the oil to the contact inlet area. In this research, an aluminium block is used as the workpiece material in an evaluation of a through pin-on-disc tribotester. Lubricating oil in the form of super olein (SO) was used in the experiment.

The results show that the friction performance during a rubbing process between a hemispherical pin and an aluminium block lubricated with SO using aluminium alloy materials, AA5083, was significantly improved.

In this study, a material that breaks down called SO, which is derived from the fractionation of palm olein, was used to use a modified aluminium micro-pit sample that will serve as a lubricant reservoir in pin-on-disc tribotester.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2023-0200/

Provide tribological information about the applicability of multi‐layer carbon‐chromium composite coatings to gears. Discuss the protection provided against scuffing failures, wear and the influence on gear power losses.

Several screening tests, such as Rockwell indentations, ball cratering, pin‐on‐disc and reciprocating wear tests, were performed in order to evaluate the adhesion to the substrate and the tribological performance of the carbon/chromium composite coating. Afterwards, twin‐disc tests were performed at high contact pressure and high slide‐to‐roll ratios to confirm the good adhesive and tribological properties of the coating under operating conditions similar to those found in gears. Gear tests were performed in the FZG machine in order to evaluate the anti‐scuffing performance of the carbon/chromium coating using additive free gear oils. Finally, the carbon/chromium composite coating was also applied to the gearing in a gearbox and its influence on the gearbox efficiency was analysed.

The C/Cr has got very good adhesion to the steel substrate, provides low friction coefficients between contacting solids in relative movement, gives excellent protection against scuffing and wear reduction in gears, and promotes a slight improvement of the gears efficiency.

The protection of this carbon/chromium coating against gear micro‐pitting should be investigated.

This study confirms the applicability of this coating to industrial gear applications, especially in two particular applications: severe applications involving high contact pressures and high sliding, frequent start‐ups and inefficient lubrication; and acting as tribo‐reactive material and substituting non‐biodegradable and toxic additives in environmental lubricants.

This work validates and quantifies the influence of this C/Cr multi‐layer composite coating in gear applications in terms of adhesion to the substrate, anti‐scuffing performance and efficiency.

Introduction From the range of engineering materials, steel finds wide application in the building construction industry. The majority of steel used is for structural purposes but thinner gauge coil and sheet products in the form of coated mild steel or stainless steel are increasingly used for cladding and roofing.

This paper aims to present a comprehensive perspective on how tribology and sustainability are related and intertwined and are linked to CO₂ emissions. This paper emphasizes on how tribological aspects affect everybody’s life and how tribological research and progress can improve energy efficiency, sustainability and quality of life.

Based upon available data and predictions for the next 50 years, the potential of tribological research and development is addressed.

The effects of tribological design can significantly increase energy savings and reduce CO₂ emissions. Taking advantage of tribological technologies and applying them to current infrastructure would have the largest energy savings coming from the transportation and power generation at 25% and 20%, respectively. Implementing these technologies can also cut down global CO₂ emissions by about 1,460 megatons of CO₂ per year in the immediate future and 3,140 megatons of CO₂ per year in the long term. The extraction and processing of resources inevitably generates CO₂. Doubling the lifetime of machine components and the use of circular economy reduces the material footprint with associated reductions in CO₂.

This perspective summarizes concisely the interrelation of tribology and sustainability with CO₂.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-09-2020-0356/