Lubricant Particles Research Articles

Wear characteristics of patterned and un-patterned tetrahedral amorphous carbon film in the presence of synthetic and bio based lubricants

In this article, wear performance of patterned and non-patterned tetrahedral carbon thin film (ta-C) is compared in the presence of various lubricants. For this purpose, wear tests were conducted at temperatures (40 °C–125 °C) which are normally found during automotive engine operation. Wear test were conducted at 100 N load and 120 min. The results showed that bio-based lubricant show better wear performance at 40 and 80 °C compared to PAO lubricant for both laser patterned and non-patterned ta-C thin film. However, at the temperature of 125 °C, PAO showed better wear performance than palm based TMP ester. This can be because of unstable film formation at higher temperatures in case of bio-based lubricant. It was also found that patterned ta-C thin films shows higher wear resistance than non-patterned thin film. This can be because of micro pores which can provide lubricant, capture micro and nano wear particle and behave as micro hydrodynamic bearings.

Effect of turning parameters on the surface of sintered self-lubricating composites

The objective of this research is to study the influence of cutting parameters on the quality and integrity of machined surfaces obtained by a longitudinal external turning in a sintered self-lubricating composite. Tests were performed at cutting speeds of 100 and 200 m/min, feed of 0.1 and 0.2 mm, and cutting depths of 0.5 and 1 mm for the materials manufactured by single and double pressing. The materials tested are composites with matrix composition of Fe-Ni-C-Si containing solid lubricants, which were subjected to the pressing process and subsequent sintering. The analysis of machined surfaces indicates that the large amount of ferrite in the microstructure of the matrix combined with the type of insert used in the tests caused high plastic deformation of the surfaces. However, solid lubricant particles were left exposed on the surfaces produced after machining. The roughness parameters Sdq (rms surface slope) and Str (texture aspect ratio) were influenced only by variations in the cutting speed. The roughness parameter Sq (root mean square height) was influenced by the variations in the cutting speed and feed as well as the material manufacturing route. Plastic deformation caused by machining led to the closing of pores, which affected the integrity of machined surfaces. The hardness of the surface boundary layer was approximately 30% higher compared with the boundary layer of sintered surfaces.

Type and concentration effects of particulate solid lubricants on the microstructure, friction, and wear of electrodeposited Ni composite coatings

Nickel–MoS2 composite coatings were obtained by electrodeposition from a nickel electrolyte containing suspended MoS2 particles. The coating composition, morphology, crystalline structure, microhardness, and frictional behavior were studied as a function of MoS2 concentration. The results obtained in this study revealed that the codeposited lubricant particles strongly influenced the composite nickel coating properties. It was found that increasing codeposited MoS2 decreases the average grain size of nickel crystallites and leads to the formation of clusters which, in turn, lead to rough coatings with a high and variable thickness. The results of tribological response indicated that the reduction of friction coefficient and the improvement of wear resistance were performed until an optimal value of MoS2 concentration, which provided the best condition that promoted the tribo-layer stability and maintained the matrix integrity. A comparison of tribological and micromechanical properties between the coating containing the optimal fraction of MoS2 particles and the coating containing nearly the same fraction of graphite particles has been undertaken. Unlike the case of the addition of graphite particles, the microhardness of composite coating has been enhanced with the incorporation of MoS2 particles. However, the incorporation of graphite particles in the coating induced more effective lubrication and wear resistance.

Influence of Temperature Variation on Tribological Behavior of Aluminum Matrix Hybrid Composites: A Statistical Analysis

The influence of temperature variation on tribological behavior of the Al 6061-10 wt.% B4C mono composite, Al 6061-10 wt.% B4C-7.5 wt.% Gr hybrid composite, and Al 6061-10 wt.% B4C-7.5 wt.% MoS2 hybrid composite was statistically analyzed in this work. The tribological studies were conducted using a high-temperature tribometer of pin-on-disk configuration, and the experiments were designed using full factorial design experimental scheme. Analysis of variance of the wear rate and friction coefficient (responses) of the hybrid composites revealed that the factors A (solid lubricant particles addition) and B (temperature) were statistically significant to influence the responses. The main effects plots revealed that the responses decreased with the addition of solid lubricant particles and increased with temperature in the range of 100-250 °C. The scanning electron microscopy analysis revealed the formation of tribolayer at 100 °C and induction of delamination and abrasion wear mechanisms.

Effect of solid lubricant particles on the tribological properties of PTFE composites lubricated with natural seawater

An orthogonal test was used to design different mixture ratios of molybdenum disulfide(MoS2), graphite, and SiO2 particles, which were filled with polytetrafluoroethylene (PTFE) composite. MoS2-, graphite-, and SiO2-modified PTFE was obtained by pressing and sintering, and the processing parameters were determined using progressive studies and experiments. The friction and wear properties of different PTFE composites lubricated with natural seawater were analyzed using an MMU-5G wear tester. A laser scanning confocal microscope was employed to examine the morphological characteristics of the worn surface. Moreover, the influence of particle proportions on the tribological property of composites was analyzed. Results show that the addition of SiO2, MoS2, and graphite can increase the bearing capacity, improve the wear resistance, reduce the friction coefficient, and increase the self-lubricating ability of the PTFE matrix.

Microstructural and tribological properties of A356 based surface hybrid composite produced by friction stir processing

Fabrication of surface hybrid composite with reinforced particles has been developed in order to enhance tribological properties of aluminum alloys. Among the aluminum alloys, increasing of tribological properties of A356 casting aluminum alloys using different reinforced particles into the surface by FSP, as a surfacing technique, is of great interest, which should be considered. Friction stir processing was attempted in order to produce a surface hybrid composite for improvement of tribological properties with alumina (Al2O3) particles and graphite (Gr) as a lubricant particles. The FSP was carried out with tool rotational speed of 1000 rpm, tool travel speed of 100 mm min−1 and tilt angle of 2° through two passes. In the present work, the structural and tribological properties of surface hybrid composite of A356 Al alloy are investigated. Structural characterization is evaluated by optical and scanning electron microscopies. Hardness and wear tests are performed in order to investigate tribological behaviors of the FSPed composite samples. The obtained results showed that the composite reinforced by Al2O3 particles exhibits higher hardness value compared to hybrid composite of Al2O3/Gr-particles because of the good bonding between Al2O3 and aluminum matrix as well as higher hardness value of Al2O3 particle itself than the Gr- particle reinforcement. In addition, wear test results depicted that the wear resistance of A356/Al2O3/Gr sample is significantly decreased compared to that of A356 Al alloy. The wear mechanism of all composites were identified adhesive wear mechanism. The reduction friction coefficient of A356/Gr composite presented higher value as opposed to the other composites.

Effect of textured surfaces created by modulation-assisted machining on the Stribeck curve and wear properties of steel-aluminum contact

Loss of machining efficiency, part repair, and replacement of mechanical components due to friction and wear is a recurring problem for performance industrial system applications. Recent studies on surface modification and micro-scale texturing have shown successful results in reducing friction and wear of lubricated surfaces. By acting as lubricant reservoirs and wear particle receptacles, micro-scale artificial surface textures positively influence lubrication regimes. In the present experimental study, a Stribeck curve is generated to compare the tribological properties of untextured and textured surfaces created by modulation-assisted machining. Aluminum 6061-T6 disks are mated with high-speed steel pins on a pin-on-disk tribometer configuration for varying speed and texture depth and density. The results suggest that the textured surfaces produced by modulation-assisted machining accelerate the appearance of the elasto-hydrodynamic regime, while also reducing friction by 56% and wear by almost 90%. The enhanced friction and wear reduction were obtained under the lower speeds studied. In general, the disk with shallower dimples presented lower values of friction under the conditions studied. No major differences were found for textures with different dimple densities.

Tribological performance of novel nickel-based composite coatings with lubricant particles

The present study is focused on the evaluation of the tribological performance of novel Ni/hBN and Ni/WS2 composite coatings electrodeposited from an additive-free Watts bath with the assistance of ultrasound. Lubricated and non-lubricated scratch tests were performed on both novel composite coatings and on standard Ni deposits used as a benchmark coating to have an initial idea of the effect of the presence of particles within the Ni matrix. Under lubricated conditions, the performance of the Ni/hBN composite coating was very similar to the benchmark Ni coating, whereas the Ni/WS2 behaved quite differently, as the latter did not only show a lower coefficient of friction, but also prevented the occurrence of stick-slip motion that was clearly observed in the other coatings. Under non-lubricated conditions, whereas the tribological performance of the Ni/hBN composite coating was again very similar to that of the benchmark Ni coating, the Ni/WS2 composite coatings again showed a remarkable enhancement, as the incorporation of the WS2 particles into the Ni coating not only resulted in a lower coefficient of friction, but also in the prevention of coating failure.

Improved wear resistance and mechanism of titanium aluminum based alloys reinforced by solid lubricant materials

Abrasion failure is a bottleneck problem that restricts the applications of titanium aluminum (TiAl) based alloys. This work has developed a facile method to endow TiAl alloys with superior wear resistance. TiAl composites reinforced by serpentine materials have been prepared by spark plasma sintering (SPS). Microstructural characterizations show that serpentine is well distributed in TiAl alloy matrix. Tribological behaviors in terms of a high-temperature friction and wear tester indicate that the reinforced particles play a positive role in decreasing wear rates and friction coefficients. Together with wear debris and high-temperature oxides, lubricant particles easily form a lubrication layer on frictional interfaces, which can help repair and compensate the worn-out pits and grooves thereby leading to the optimal wear resistance with the lowest friction coefficient of 0.41 and wear rate of 1.97 × 10−4 mm3/(Nm) at 400 °C–600 °C. This work sheds insights into evaluating the practicability of serpentine as a desirable solid lubricant and providing guidance for designing other serpentine-reinforced composites.

폴리우레탄 유압 왕복 씰의 파손 진전 특성

In this work, the degradation progression of a polyurethane (PU) hydraulic reciprocating seal with respect to the sliding distance were investigated using a pin-on-reciprocating tribo-tester. Also, the acceleration effect of alumina particles added in lubricant on degradation of PU seal were assessed, with an aim to contribute to the development of accelerated wear testing methods. As a result, It was shown that the height of PU specimens decreased drastically at the initial stage of sliding. Then, the height decrease was found to become gradual as sliding distance further increased. The result also shows that the height decrease of the PU specimen was mainly due to the effect of the compression set and wear. In addition, the noted abrasive wear of the PU specimens was found to be significantly accelerated due to the alumina particles in lubricant, which determined a further result in 50 % faster height decrease with increasing sliding distance, as compared to the normal lubricant. The outcome of this work may provide significant and useful information for the prediction of the lifetime of a hydraulic reciprocating seal, and for the continued development of accelerated wear testing of the hydraulic reciprocating seal.

Quantification of lubrication and particle size distribution effects on tensile strength and stiffness of tablets

We adopt a Quality by Design (QbD) paradigm to better control the mechanical properties of tablets. To this end, the effect of particle size distribution, lubricant concentration, and mixing time on the tensile strength and elastic modulus of tablets is studied. Two grades of lactose, monohydrate and spray-dried, are selected. Tablets are compressed to different relative densities ranging from 0.8 to 0.94 using an instrumented compaction simulator. We propose a general model, which predicts the elastic modulus and tensile strength envelope that a specific powder can obtain based on its lubrication sensitivity for different particle size distributions. This is possible by introducing a new dimensionless parameter in the existing tensile strength and elastic modulus relationships with relative density. A wide range of lubrication conditions is explored and a predictable model is calibrated. The mechanical properties of lactose monohydrate tablets are noticeably dependent on particle size, unlike spray-dried lactose where little to almost no sensitivity to particle size is observed. The model is designed in a general fashion that can capture mechanical quality attributes in response to different lubrication conditions and particle size, and it can be extended to powders than undergo different deformation mechanisms, complex mixtures, and doubly convex tablets. Therefore, the model can be used to map the achievable design space of any given formulation.

A three-dimensional model for lubricant depletion under sliding condition on bit patterned media of hard disk drives

In this paper, we model the depletion dynamics of the molecularly thin layer of lubricants on a bit patterned media disk of hard disk drives under a sliding air bearing head. The dominant physics and consequently, the lubricant depletion dynamics on a patterned disk are shown to be significantly different from the well-studied cases of a smooth disk. Our results indicate that the surface tension effect, which is negligible on a flat disk, apparently suppresses depletion by enforcing a bottleneck effect around the disk pattern peak regions to thwart the migration of lubricants. When the disjoining pressure is relatively small, it assists the depletion. But, when the disjoining pressure becomes dominant, the disjoining pressure resists depletion. Disk pattern orientation plays a critical role in the depletion process. The effect of disk pattern orientation on depletion originates from its complex interaction with other intermingled factors of external air shearing stress distribution and lubricant particle trajectory. Patterning a disk surface with nanostructures of high density, large height/pitch ratio, and particular orientation is demonstrated to be one efficient way to alleviate the formation of lubricant depletion tracks.

Sliding Wear Behavior Solid Lubricant Based Ni–Al–Bronze Surface Composite Developed by Friction Stir Processing

In this study, a nickel aluminium bronze (NAB) metal matrix composite reinforced with solid lubricants i.e. graphite and molybdenum disulphide (MoS2) was prepared by friction stir processing. Friction stir processing (FSP) refined the grain structure as compared to the as-cast NAB. The micrographs of graphite reinforced matrix revealed fine globular α phase with some elongated morphology α phases, whereas MoS2 reinforced surface composite mainly exhibited fine α phase particles. FSP also resulted in the distribution of solid lubricant particles in the NAB matrix. The hardness of the composites decreased with the addition of the solid lubricants in NAB matrix. SEM–EDS analysis of the reinforced NAB matrix confirmed the presence of solid lubricants. The influence of solid lubricants on the sliding wear behavior of NAB metal matrix was investigated by using the design of experimental approach. The experimental results revealed better wear resistance of the NAB–MoS2 surface composite as compared to graphite reinforced and FSPed NAB surface. SEM–EDS analysis of worn out surfaces and wear debris were carried out for understanding the wear mechanism.

Influence of Surface Finishing on the Tribological Behavior of Self-Lubricating Iron-Based Composites

ABSTRACTRecently, we presented the tribological evaluation of self-lubricating sintered steels produced by taking advantage of the powder injection molding process, the recently introduced plasma-assisted debinding and sintering process, and the in situ formation of solid lubricant particles. This new processing route promotes the in situ generation of nanostructured turbostratic graphite particles during silicon carbide dissociation. In this work, we present the influence of surface finishing on the tribological behavior of self-lubricating composites sintered at 1150°C with (3 and 5 wt%) and without SiC additions. We discuss the effects of the surface topography (Ra) on the friction coefficient and wear rates of specimens and counterbodies. The tribological behavior was analyzed using linear reciprocating sliding tests (constant load of 7 N, 60-min duration). It was shown that the reduction in surface roughness increased both the friction coefficients and wear rates of specimens and counterbodies, probably due to plastic deformation and consequent graphite reservoir sealing. Chemical analyses of the wear scars using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis showed a tribolayer that was composed predominantly of carbon and oxygen. Analyses of the wear scars showed traces of plastic deformation on both samples and counterbodies and the predominance of abrasion as the main wear mechanism.

Microstructural Characterization of Solid State Reaction Phase Formed During Sintering of Hexagonal Boron Nitride with Iron.

In the development of dry self-lubricating composites, not only solid lubricant particle size and distribution are important, but also the correct selection of the solid lubricant characteristics, which should be stable, i.e. not reactive, during the whole processing. In this work, Fe+9 vol% h-BN composites were produced by uniaxial cold compaction and sintering, for which a reaction between h-BN and iron was detected after sintering at 1,150°C. The reaction phase was characterized by optical and scanning electron microscopy and identified by X-ray diffraction and energy-dispersive X-ray spectroscopy. The newly formed phase had high hardness when compared with the iron matrix. The resulting composites presented a high friction coefficient and high wear.

Review of Nickel-Based Electrodeposited Tribo-Coatings

Among various methods used for protecting the industrial components from wear/abrasion failures, electrodeposition has attracted considerable attention in recent years because of its advantages such as being efficient, accurate, affordable, and easy to perform. In this regard, electrodeposition of nickel-based composite and alloy coatings is an inexpensive method compared with other coating methods such as chemical vapor deposition and physical vapor deposition. Furthermore, nickel-based composite electrodeposition is an eco-friendly substitute for conventional toxic coatings such as hard chrome. Embedding hard particles within the metallic matrix improves the wear resistance by increasing the ductility of the matrix in the contact area, changing the preferred grain growth direction to close-packed directions, and boosting dispersion and grain-refinement strength. In addition, lubricant particles provide superior anti-abrasive behavior because of their non-sticky nature. Several factors affect the incorporation of the particles into the electrodeposited coating and therefore the wear behavior of these coatings is related to different parameters such as current density, bath composition, pH, amount and size of the embedded particles. This review paper provides an overview of the wear behavior of nickel-based electrodeposited coatings including their composites and alloys with the focus on the parameters affecting wear rate, coefficient of friction, hardness, and roughness.

Effect of Liquid Phase during Sintering on Mechanical and Tribological Properties of Self-Lubricating Composites

The present work aimed to contribute to the development of high performance self-lubricating sintered composites, with low friction coefficient and high mechanical strength. Self-lubricating composites presenting embedded solid lubricants in a ferrous matrix were produced. Hexagonal boron nitride (hBN) and graphite were the solid lubricants powders added during the mixing step. The composites were processed by conventional powder metallurgy. The liquid phase sintering, by adding copper, improved the degree of continuity of the matrix by rearranging the solid lubricant particles. With this, besides the hardening effect on the matrix, the mechanical properties of the composites were improved, with tensile strength increasing when compared to the same composite without copper. By using the proposed methodologies, optimized composites presenting friction coefficient of 0.12, tensile strength of 500 MPa and scuffing resistance of 29300 N.m were obtained.

Improving tribological behavior of friction stir processed A413/SiCp surface composite using MoS2 lubricant particles

The effect of MoS2 lubricant particles on the microstructure, microhardness and tribological behavior of A413/SiCp surface composite, fabricated via friction stir processing (FSP), was studied. For this purpose, the FSP was carried out with tool rotational speed of 1600 r/min, tool travel speed of 25 mm/min and tool tilt angle of 3° through only a “single pass”. The optical and scanning electron microscopies, microhardness and reciprocating wear tests were used to characterize the samples. The results showed that the addition of MoS2 lubricant particles to A413/SiCp surface composite leads to the decrease of friction coefficient and mass loss. In fact, the generation of mechanically mixed layer (MML) containing MoS2 lubricant particles in A413/SiCp/MoS2p surface hybrid composite results in the reduction of metal-to-metal contact and subsequently leads to the improvement of tribological behavior.

Experimental Investigation and Optimization of Dry Sliding Wear Parameters on Solid Lubricant Reinforced Bronze Matrix Composites - A Taguchi Approach

This present study aims to investigate the dry sliding wear behaviour of tungsten disulfide (WS2) particle reinforced bronze matrix composite against surface hardened steel and to discover the optimum wear parameter values such as applied load, sliding distance, sliding velocity and volume fraction of reinforcement to reduce the specific wear rate. The composite specimens were fabricated by liquid metallurgy route by varying the volume fraction of solid lubricant particles and prepared as per American Society for Testing of Materials (ASTM) G99-95. The experiments were carried out based on Taguchi design of experiments technique with L27 orthogonal array. The wear tests were conducted in pin-on disc wear testing machine for different loads - 20N, 40N and 60N, sliding velocities - 2.09m/s, 2.62 m/s and 3.14m/s and sliding distances of 600m, 1200m and 1800m in unlubricated conditions. The significant influence of wear parameters on sliding wear, interactions and optimum combination of wear parameter values to minimize the wear rate were obtained by signal-to-noise (S/N) ratio and analysis of variance (ANOVA). The results demonstrated that inclusion of tungsten disulfide particles decreased the wear rate of bronze and also the increases in amount of secondary phase increase the wear resistance of composites. The effect of solid lubricant particle on interfacial temperature was also studied and reported. It was found that percentage of solid lubricant and load are the most significant factors influencing the friction and wear properties of composites. The results revealed that, WS2 particle reinforced bronze matrix composites were the potential component can be replaced for pure bronze products in wear resistance applications.

Tribological studies to analyze the effect of solid lubricant particle size on friction and wear behaviour of Ti-6Al-4V alloy

In modern industry, mechanical parts are subjected to friction and wear, leading to heat generation, which affects the reliability, life and power consumption of machinery. The study of lubricant film formed between various geometric shapes are inherently complicated and interconnected, making it necessary to understand the concepts of tribological phenomena. To overcome the tribological losses due to friction and wear, use of lubricants with high viscosities and lower evaporation makes relative motion between two surfaces very smooth. Advancement in modern tribology has facilitated the use of applying solid lubricants in various industrial applications. Solid lubricants in ample thickness can effectively work under extreme conditions of temperature, loads and speeds. The effectiveness of solid lubricant particles strongly depends on the type of lubricant used in the suspension, solid lubricant particle size, and as well as concentration. In view of this, the present investigation aims to develop MoS2 suspension with different weight fractions and to analyze tribological properties in order to make it suitable for most industrial applications. To characterize the same, an experimental setup has been developed to observe and measure the lubricant film thickness at various particles size and concentrations of solid lubricants. To determine Extreme Pressure (EP) properties of applied solid lubricants, EP test (ASTM D2783) experiments were performed on a four-ball tester. The results obtained from the experiments show the use of the solid lubricant with lesser particle size provide effective thin film thickness in comparison with larger particle size. The results indicate that the optimum particle size and concentration of suspended MoS2 solid lubricants improve the tribological properties with an intended life time of the surfaces.