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The purpose of this paper is to examine the practicability of the self-designed ambient humidity controllable pin-disc/rolling multifunctional friction and wear test device and to evaluate the friction and wear characteristics of materials under diverse ambient humidity conditions in different contact forms.

The practicability of the self-designed multifunctional friction tester was examined by the friction and wear tests of materials under different ambient humidity conditions [65%RH, 98%RH (relative humidity)] in diverse contact forms (pin/disc and rolling). Meanwhile, the friction and wear properties of pin/disc samples also rolling samples were assessed from three aspects: average friction coefficient, wear mass and wear morphology.

The results prove that the self-designed multifunctional friction tester has practicability. Therefore, it can be used to simulate the friction and wear tests of materials under diverse ambient humidity conditions in different contact forms. Besides, it is evident that the wear damage of pin/disc and rolling samples are greatly improved under high ambient humidity conditions. And when other conditions are identical, the higher the ambient humidity, the smaller the average friction coefficient, wear mass and wear damage degree of pin/disc also rolling samples.

This paper offers a self-designed multifunctional friction and wear test device. And the tester not only can realize the control of test ambient humidity, but also achieve the wear test of pin/disc or rolling contact forms. The design and production of the tester can offer convenience for the research of tribology, and provide fundamental guidance for the study of materials under high humidity condition in diverse contact forms.

This paper aims to determine a suitable anti-wear and friction-reducing compounding additive for lithium greases (LG) by investigating the effects of three single additives potassium borate (PB), zinc dialkyl dithiophosphate and molybdenum dialkyl dithiophosphate (MoDDP) and two compound additives on the friction, wear and extreme pressure properties of LG.

The effects of the above five additives on the friction, wear and extreme pressure properties of LG were investigated using an SRV-5 friction tester. An X-ray photoelectron spectrometer was used to analyze the various elements presented on the wear surface as well as the types of compounds.

The compound additive suitable for grease consists of PB and MoDDP, which have excellent friction reduction, anti-wear and extreme pressure properties. And a boundary protection film consisting of oxide and MoS₂ is formed on the friction surface, thus improving the friction reduction and anti-wear performance of the grease.

This study can improve the anti-wear and friction-reduction performance of greases, which is of great importance in the field of industrial lubrication. The results of this paper are expected to be useful to researchers and academics of grease.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-11-2022-0350/

This study aims to investigate the effect of MoS2 powder on tribological properties of sliding interfaces.

Loose MoS2 powder was introduced in the gap of point-contact friction pairs, and sliding friction test was conducted using a testing machine. Friction noise, wear mark appearance, microstructure and wear debris were characterized with a noise tester, white-light interferometer, scanning electron microscope and ferrograph, respectively. Numerical simulation was also performed to analyze the influence of MoS2 powder on tribological properties of the sliding interface.

MoS2 powder remarkably improved the lubrication performance of the sliding interface, whose friction coefficient and wear rate were reduced by one-fifth of the interface values without powder. The addition of MoS2 powder also reduced stress, plastic deformation and friction temperature in the wear mark. The sliding interface with MoS2 powder demonstrated lower friction noise and roughness compared with the interface without powder lubrication. The adherence of MoS2 powder onto the friction interface formed a friction film, which induced the wear mechanism of the sliding interface to change from serious cutting and adhesive wear to delamination and slight cutting wear under the action of normal and shear forces.

Tribological characteristics of the interface with MoS2 powder lubrication were clarified. This work provides a theoretical basis for solid-powder lubrication and reference for its application in engineering.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-04-2020-0150/

The purpose of this paper is to present the results of research into using an additive to SAE 15W/40 engine oil during operation and its influence on lubricating properties (normalised tests) on weld point Pz, non-seizure load Pn, load wear index Ih and on seizure load Pt. The friction pair consisted of a group of four balls and the tested lubricant. Moreover, the author tested the influence of an additive to engine oil (non-normalised tests) on tribological properties, including friction force, wear and the temperature of friction area for the C45 steel/210Cr12 steel friction joint. She also determined the influence of an additive to engine oil on the formation of the operating surface layer. The research results helped to build the model of the boundary layer that was formed as a result of adding an additive to engine oil.

The lubricant properties of engine oil and engine oil to which an additive was added during operation were determined according to PN-76/C-04147. The following are the indexes of lubricant properties: weld point Pz, load wear index Ih, non-seizure load Pn, seizure load and average scar diameter. The Pz, Pn and Ih indexes were determined at abruptly increasing load to the moment of welding of the friction pair. The Pt index was determined at the increasing load of the friction pair from 0 to 800 daN at the speed of 408.8 N/s. The tests of tribological properties (friction force, wear and the temperature of friction area) were conducted for the C45/210 Cr12 friction pair in the presence of a lubricant and a lubricant with an additive.

The modification of SAE 15W/40 engine oil with the additive added during operation resulted in improved indexes of lubricant properties Pz, Pn, Ih and Pt and average scar diameter. The boundary layer for the modified oil breaks after a longer time and at lesser friction force. The modification of the engine oil reduced the wear of the friction pair. After the friction process, element composition in the surface layer of the wear trace and its distribution were determined in relation to applied lubricants. A significant amount of sulphur, phosphorus and oxygen, as well as an insignificant amount of copper, was observed in the wear trace after the friction process in the presence of the lubricant medium. The distribution of elements in the wear trace when the engine oil with the additive was used is steady in the wear trace and outside it. Some sulphur, phosphorus and chlorine were found in the wear trace.

The results of tests on tribological properties (non-normalised tests) confirmed the positive affect of the additive to engine oil on lubricant properties (normalised tests). The modification of the engine oil caused reduced friction force and the reduced wear of the friction pair. The reduction of friction force and wear was the result of the formation of the surface of a greater amplitude density of unevenness tops in the friction process. Moreover, the operating surface layer, created in the friction process when the additive was added to the engine oil, had greater load participation at 50 per cent C. This operational surface layer improved tribological properties, i.e. it reduced value of friction force and wear. The test results were used to build a model of the boundary layer created as a result of the additive added to engine oil.

This paper aims to study the micro-structure evolution of friction layers to optimize the friction and wear behaviors of TiAl-based material. It further enlarges the scope of using TiAl alloys and increase in the service life of TiAl alloy-made mechanical components, especially under some extreme conditions.

To study the structure evolution of friction layers, the HT-1000 tribometer is used to study the friction and wear properties of as-prepared samples. With the assistance of field emission scanning electron microscopy and an electron probe micro-analyzer, the stratified structures in cross-sections and a surface morphology of the wear scars are well characterized. A ST400 surface profiler helps in better understanding of the three-dimensional texture profiles of wear scars. X-ray diffractometer (XRD) is also used to analyze phases in the as-prepared samples.

An analysis method on the micro-structure evolution can provide better views to understand the influence of friction layers on the tribological behavior, at different wear stages. It finds that the micro-structure evolution of friction layers has an immediate effect on the friction coefficients and wear rates of TiAl-based material. It also proves to be a useful tool for evaluating the behaviors in friction and wear of TiAl-based material.

The findings of this paper provide better assistance to explore the effect of friction layers on the friction and wear behaviors of TiAl-based materials. The results help in deep understanding of the micro-structure evolution of friction layers. It also increases the service life of TiAl-based mechanical components.

The purpose of this paper is to investigate the effect of reciprocating and unidirectional sliding motions on friction and wear of phenolic resin-based composite.

The phenolic resin-based composite was fabricated by hot press molding, and then the tribological properties were tested on a CSM tribometer with two types of friction motion modes – reciprocating friction and unidirectional friction.

The results showed that the composite exhibited low friction coefficient in unidirectional test. However, the wear factor recorded under unidirectional sliding condition was 12-16 times higher than the reciprocating friction results. The SEM and optical microscopy test results showed that changing the relative motion mode resulted in different topography of transfer film, which is responsible for the different friction and wear characteristics of the composite under reciprocating and unidirectional friction conditions.

Effect of different friction modes, reciprocating friction and unidirectional friction, on friction characteristics of the composite is sought. Different topography of transfer film formed under reciprocating and unidirectional friction conditions contributed to the different friction characteristics.

The effect of different service parameters on the current-carrying tribological properties of CF-Al₂O₃/Cu composites was investigated, and the damage behavior of the composites under different service parameters was probed. The purpose of this study is to provide a theoretical basis for the application of CF-Al₂O₃/Cu composites.

The composites were fabricated by internal oxidation combined with powder metallurgy. The current-carrying tribological properties of CF-Al₂O₃/Cu composites were investigated on an electrical damage test system at different loads and currents.

As the load increases, the wear mechanism of the composite changes from abrasive wear to delamination wear. As the current increases, the oxidation wear and arc erosion of the composites gradually intensified. Under the service parameters of 0–25 A and 30–40 N, the composite has relatively stable current-carrying tribological properties.

This paper could provide a theoretical basis for the practical application of CF-Al₂O₃/Cu composites.

This paper aims to thrash out friction and wear properties of automobile brake lining reinforced by lignin fiber and glass fiber in braking process.

ABAQUS finite element software was used to analyze thermo-mechanical coupled field of friction materials. XD-MSM constant speed friction testing machine was used to test friction and wear properties of friction material. Worn surface morphology and mechanism of friction materials were observed by using scanning electron microscope.

The results show that when the temperature was below 350°C, worn mechanism of MFBL was mainly fatigue wear and abrasive wear, and worn mechanism of GFBL was mainly fatigue wear because MFBL contained lignin fiber. Therefore, it exhibits better mechanical properties and friction and wear properties than those of GFBL.

Lignin fiber can improve mechanical properties and friction and wear properties of the automobile brake lining.

The purpose of this study is to investigate the effect of iron content on the friction and wear performances of Cu–Fe-based friction materials under dry sliding friction and wear test condition.

Cu–Fe-based friction materials with different iron content were prepared by powder metallurgy route. The tribological properties of Cu–Fe-based friction materials against GCr15 steel balls were studied at different applied loads and sliding speeds. Meanwhile, microstructure and phases of Cu–Fe-based friction materials were investigated.

Cu–Fe-based friction materials with different iron content are suitable for specific applied load and sliding speed, respectively. Low iron content Cu–Fe-based friction material is suitable for a high load 60 N and low sliding speed 70 mm/min and high iron content Cu–Fe-based friction material will be more suitable for a high load 60 N and high sliding speed 150 mm/min. The abrasive wear is the main wear mechanism for two kinds of Cu–Fe-based friction materials.

The friction and wear properties of Cu–Fe-based friction materials with different iron content were determined at different applied loads and sliding speeds, providing a direction and theoretical basis for the future development of Cu–Fe-based friction materials.

Random point-contact between the space bearing retainer and the rolling elements may cause wear of the space bearing retainer. The paper aims to clarify the friction and wear behaviors of polyimide bearing retainer under point-contact condition.

Space bearing retainers were cut into flat specimens and the tribological behaviors of the specimens were studied under point-contact condition using a friction and wear testing machine. Different sliding velocities and normal loads were used to simulate the running state of space bearing retainer. The wear behaviors of the space bearing retainer were analyzed by SEM and white light interferometer.

The friction coefficient of the polyimide composites decreased with increase in sliding velocity from 1  to 5 mm/s. Moreover, with increase in sliding velocity and normal load, the wear rate of the polyimide composites decreased and increased, respectively. Moreover, the wear behaviors of the polyimide composites were mainly determined by the combined actions of ploughing friction and adhesive friction. The lubricating properties of transfer film and wear debris were limited under point-contact condition.

The paper includes implications for the understanding of the wear mechanism of the polyimide composites space bearing retainer under point-contact condition and then to optimize space bearing retainer materials further.

Under point-contact condition, wear debris can hardly participate in the friction process because of limited contact area. Consequently, the wear debris has limited impact on the wear process to decrease the friction and wear.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-01-2020-0017/