Wear Reduction Mechanism Research Articles

Mechanisms of remarkable wear reduction and evolutions of subsurface microstructure and nano-mechanical properties during dry sliding of nano-grained Ti6Al4V alloy: A comparative study

A comprehensive investigation into dry sliding wear and associated evolutions of subsurface microstructure and nano-mechanical properties of a bulk nano-grained Ti6Al4V alloy (NG-Ti6Al4V) was conducted. Comparing with its coarse-grained counterpart (CG-Ti6Al4V), NG-Ti6Al4V always exhibited lower friction coefficient and greater wear resistance in a wide range of tribological conditions. It was also found that the sliding wear induced nano-mechanical properties and microstructure evolutions in Ti6Al4V alloy were largely dependent on its initial microstructural features. For the first time, TEM observations provided a direct experimental evidence that the originally saturated nanostructure in NG-Ti6Al4V could be further refined by sliding wear. This study proposed an effective strategy to improve the load-bearing ability of Ti6Al4V alloy by producing bulk homogeneous nanostructure.

High temperature induced “glaze” layer formed in HVOF-sprayed NiCrWMoCuCBFe coating and its wear reduction mechanism

The in-situ formation of oxides on alloy surface induced by high temperature can effectively reduce wear and resist oxidation. In consideration of the solid solution strengthening effect and great oxidation resistance of additional elements at elevated temperature, the NiCrWMoCuCBFe coating was prepared by high velocity oxygen flame (HVOF) spraying technology, and its tribological behavior was scrutinized from 25 to 800 °C. By means of high temperature Vickers hardness tester and high temperature X-ray diffractometer, the mechanical properties and microstructures of NiCrWMoCuCBFe coating were measured. And the effect of the mechanical properties and microstructures of the coating on tribological performance was discussed in detail. The results showed both its friction coefficient (0.37) and wear rate (5.067 × 10−6 mm3·N−1·m−1) at 800 °C were the lowest, which was mainly related to the formation of “glaze” layer on the coating surface at high temperature. The glaze layer consisted of two parts, which were NiCr2O4 oxide film with the ability of interlaminar slip formed in the outer layer and nano-grains existed in the inner layer. Worth mentioning, these nano-grains provided bearing capability while the oxide film was vital to reduce wear rate and friction coefficient. As the ambient temperature increased, many hard oxides were produced on the wear scars, including NiO, Cr2O3, MoO3, and Mo2C. They can improve tribological and mechanical properties of NiCrWMoCuCBFe coating at a wide temperature range.

Synergetic effect of surface texturing and graphene nanoplatelets on the tribological properties of hybrid self-lubricating composite

In the present work, investigation is carried out to study the combined effect of graphene as a solid lubricant (SL) and surface texturing (ST) on the friction and wear reduction mechanism of hybrid aluminum composite and chromium plated chrome steel tribo pairs. The friction and wear behavior of nontextured surface (NTS) and textured surface (TS) were analyzed under dry sliding conditions (DSC) and lubricated conditions (LSC). All TS displayed a lower coefficient of friction (COF) and wear volume than the NTS sample. T2 texture reveals 63.88%, 70.53% and 44.99% decrease in COF and indicates a decrease of 32.13%, 60.30%, and 86.03% in wear volume than the NTS under DSC and LSC (virgin PAO-4; SAE20W50), respectively.

Simultaneous laser in-situ generation of graphene and micro-textures on ductile iron and their effects on tribological properties

In this study, a picosecond (ps) laser was employed to produce micro-textures on ductile iron in linearly processing leading to significantly higher processing efficiency. The fabrication efficiency was increased about 1331 times as compared to the more common spot-by-spot texturing method. The ps laser induced graphene (LIG) structures were simultaneously fabricated in dimples, which further enhanced the surface tribological properties. The surface micro-textures were produced by forming micro-dimples on the substrate via the laser ablation process. The dimple diameter and area density were regulated by varying the key laser processing parameters, and were experimentally correlated to the tribological properties of the ductile iron substrate. To understand deeper into the wear reduction mechanism of the micro-dimples, simulation models based on the Reynold equation were established, which analyze the flow field pressure distribution and demonstrate the hydrodynamic lubrication effect of the micro-textures. The ball-on disk friction test showed that the area density of the micro-textures had a significant influence on the friction and wear properties. The micro-texture with the area density of 20% and the average dimple diameter of 36 μm showed the highest volume wear rate reduction of 70% and the friction coefficient reduction of 20% respectively. The results indicated that the simultaneous laser in-situ generation of graphene micro-textures is an effective way of enhancing tribological properties on the ductile iron surface. It enhances the hardness of textured surfaces, thermal diffusion, debris capture ability, and fluid dynamic lubrication effect.

An Evaluation of the Tribological Behavior of Cutting Fluid Additives on Aluminum-Manganese Alloys

The introduction of additives enhances the friction and wear reduction properties of cutting fluids (CFs) as well as aids in improving the surface quality of the machined parts. This study examines the tribological behavior of polymer-based and phosphorus-based additives introduced into cutting fluids for the machining of Al-Mn alloys. Ball-on-disc tests were used to evaluate the coefficient of friction (COF) and lubrication failure temperature to study the performance of the additives in the cutting fluids. Surface characterization was performed on the sliding tracks induced on the Al-Mn disc surfaces and used to propose the wear and friction reduction mechanisms. The polymer-based additive possessed a higher temperature at which lubrication failure occurred, displayed comparable COF at a lower temperature under certain conditions, and possessed a steadier tribological behavior. However, the phosphorus-based additive was observed to display lower COF and wear damage from 200 °C till failure. The lower COF values for the phosphorus-based additive at 200 °C corresponded with lower surface damage on the Al-Mn surface. The phosphorus-based additive’s performance at 200 °C could be attributed to the forming of a phosphorus-rich boundary layer within the sliding wear track, resulting in less surface damage on the Al-Mn surface and lower material transfer to the counterface steel ball surface.

Tribological performances of hybrid composites of Epoxy, UHMWPE and MoS2 with in situ liquid lubrication against steel and itself

In this paper, hybrid polymeric composites of epoxy with two solids (UHMWPE and MoS2) and one liquid (base oil SN150) fillers were prepared to improve the thermal, mechanical and tribological properties for load bearing applications. Due to relatively high friction of solid lubricants compared to liquid lubricants, base oil was incorporated into the epoxy composite as liquid filler to achieve enhanced tribological properties. All the experiments were conducted with two interfacial conditions: polymer composite against steel (EN31) and polymer composite against itself. The base oil-filled epoxy composite showed excellent tribological performance with specific wear rate in the range of 10−7 mm3/Nm and low coefficient of friction of 0.08–0.1 at a constant nominal contact pressure of 0.611 MPa and speed 1 m/s. Durable transfer film formation was identified as the main wear reduction mechanism. These fillers also made the surface of epoxy hydrophobic in nature which reduced adhesion and friction. By adding fillers, thermal degradation temperature of the composite was increased by 22.8%. The lubrication mechanism was identified as mixed lubrication with three different sub-regimes.

Cutting Behavior of Self-Lubricating Ceramic Tool in Dry Machining of 40Cr Quenched Steel

In this paper, the dry cutting performance of Al2O3/TiC-based ceramic composites with nanoCaF2 was studied. Compared with the Al2O3/TiC ceramic tool, the Al2O3/TiC/CaF2 ceramic tool has lower cutting force, cutting temperature and surface roughness when milling 40Cr hardened steel. Three cutting parameters of cutting speed, feed per tooth, and cutting depth were used to conduct orthogonal experiments to study its changing trend. Through testing of cutting force, cutting temperature and surface roughness, and by comparison with ceramic tools without nanosolid lubricant added, the order of influence of three cutting parameters on cutting force, cutting temperature and surface roughness was obtained. The experimental results showed that the cutting force, cutting temperature and surface roughness of Al2O3/TiC/CaF2 ceramic tools containing nanoCaF2 werebetter than those of Al2O3/TiC ceramic tools. The cutting force, the cutting temperature, and the surface roughness were respectively reduced by 16.5%, 25.8% and 43% compared to when no solid lubricant was added. In addition, after adding solid lubricant, the effect of cutting depth on cutting force was significantly reduced. The average friction coefficient of the tool rake surface was 31.1% lower than that of ceramic tools without solid lubricant. In order to explain this phenomenon, through scanning electron microscopy (SEM) scanning and energy spectroscopy (EDS) elemental analysis, the wear reduction mechanism of solid lubricants was analyzed, that is, during the cutting process, nanosolid lubricants precipitated and formed lubricating film on the rake surface of the tool to reduce the friction coefficient. This was also the main reason for reducing the cutting temperature.

Mechanisms of friction and wear reduction by h-BN nanosheet and spherical W nanoparticle additives to base oil: Experimental study and molecular dynamics simulation

Hexagonal boron nitride (h-BN) nanosheets, spherical W nanoparticles, and their combinations were utilized as lubricant additives to synthetic PAO6 oil. The addition of W NPs led to a decrease in the coefficient of friction and wear rate. Molecular dynamics (MD) simulations and in situ TEM mechanical tests showed that the positive effect of adding spherical W NPs can be attributed to their rolling and sliding in the tribological contact zone. Adding BN nanosheets to PAO6 also improved the tribological performance of friction pairs: MD simulations suggest that the exfoliation and sliding of BN layers under tribological contact can contribute to the reduction of friction and wear. Moreover, a synergistic effect from the simultaneous addition of W and BN nanoparticles was observed: the CoF and wear reached minimum values among all tested suspensions. The formation of W/BN core/shell structures by wrapping of W nanoparticles by h-BN sheets provided superior macroscale lubricity.

Investigation of tribological properties of two protic ionic liquids as additives in water for steel–steel and alumina–steel contacts

Water-based lubricants are attractive owing to their low cost and eco-friendliness. An appropriate additive package must be considered to use water as a lubricant. Recently, protic ionic liquids (PILs) were emphasized for improving the lubricity of water. Most PILs are nontoxic and biodegradable. In this study, tert-octylamine oleate and diethanolamine oleate PILs were investigated by using them as additives (1% wt.) in water. Their lubrication properties were tested on a ball-on-plate reciprocating tribometer using steel-steel and alumina-steel friction pairs. The investigated PILs improved water's friction and wear reduction ability up to 80%. Both friction pairs performed similarly. However, the alumina-steel friction pair exhibited a more stable friction. The adsorption layer was assumed the most likely friction and wear reduction mechanism.

Tribological characteristics and micromilling performance of nanoparticle enhanced water based cutting fluids in minimum quantity lubrication

Friction and wear characteristics of water-based nanofluids were studied. Deionized water-based nanofluids were prepared with alumina (Al2O3), hBN, MoS2, and WS2 nanoparticles. Tribological study of the prepared nanofluids was undertaken on a ball-on-disk tribometer in minimum quantity lubrication (MQL) mode on Ti-6Al-4 V workpiece. The effect of flow rate on the coefficient of friction (μ) and wear of the workpiece was reported for different nanofluids. 3D profiles of the wear tracks were obtained to study the wear depth and wear profile. Alumina-based nanofluids have shown excellent performance in terms of friction and wear as compared to the other nanofluids. The coefficient of friction, wear track depth and specific wear were reduced by 53.89 %, 23.4 %, and 37.03 % respectively for alumina nanofluid in MQL mode as compared to the dry environment. A commercial cutting fluid (UNILUB 2032) was used for comparative studies. The commercial cutting fluid performed slightly better than the alumina nanofluid, both used in MQL mode. Even though hBN, MoS2, and WS2 are solid lubricants, their performance as nanofluids in MQL mode was not better than alumina nanofluids. Alumina particles, being spherical shaped, were able to provide better lubrication owing to the ball-bearing effect. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) of the wear tracks were conducted to understand the mechanism of friction and wear reduction. Micromilling experiments were done on Ti-6Al-4 V using the prepared cutting fluids in MQL mode to evaluate their effect on machining forces and burr formation. Alumina nanofluids and the commercial lubricant have shown significant reduction in machining forces and burr formation as compared to the other nanofluids. This is in correlation to the tribological performance of these cutting fluids.

Study of the effect of surface laser texture on tribological properties of cemented carbide materials

Surface texturing has become a potential method to obtain a low friction coefficient under dry/lubricated conditions for different mechanical product surfaces. The mechanism of friction and wear reduction from a micro-texture on the surface of cemented carbide cutting tools was investigated by dry cutting a titanium alloy. Three kinds of micro-textures, namely, line, sinusoidal and rhombic grooves, with different area occupancy rates were produced by a laser on the cemented carbide surface. Experiments and finite element simulation of ABAQUS were used to investigate the tribological characteristics of micro-textured cemented carbide. The results indicated that the line-textured cemented carbide with an area occupancy rate of 10% showed a low friction coefficient of 0.076, which is approximately 34% of the non-textured sample. Few adhesives appeared on the textured surface, while a large number of adhesives were attached to the smooth surface after 30 min of dry friction between the cemented carbide and the titanium alloy balls. Moreover, among the three textures, the line-groove texture has the smallest friction coefficient and a good anti-wear effect. The results show that the existence of a groove texture can effectively reserve the wear debris, reduce the bond wear and weaken the furrow effect.

Wear reduction mechanisms within highly wear-resistant graphene- and other carbon-filled PTFE nanocomposites

In recent years, a few select carbonaceous fillers with nanometer-size dimensions, such as graphene platelets, activated carbon nanoparticles and carbon nanotubes, have been shown to reduce the wear rates of PTFE to levels approaching 10−7 mm3/Nm and below. X-ray diffraction (XRD) and attenuated total reflectance (ATR) mode IR spectroscopy are used to show that these highly effective fillers provide wear resistance to PTFE through shared mechanisms. These mechanisms are also shown to operate in highly wear-resistant composites of PTFE with nanometer-sized particles of α-phase alumina. Addition of these highly effective fillers to PTFE results in a greater resemblance of the crystalline structure of PTFE at room temperature with a tougher and higher temperature phase. When slid against steel countersurfaces under ambient conditions, these fillers embedded within the PTFE matrix also enable the formation of robust transfer films through the formation of metal chelates.

Roles of nanomaterials at the rubbing interface of mechanical systems

Abstract The primary role of lubricant oil is to reduce friction and wear of rubbing interface. However, these lubricants often cannot meet the performance requirements of relatively sliding mechanical elements due to the change in viscosity over the period of time and operating conditions. This article summarizes the recent progress on the friction and wear reduction mechanisms of different additives suspended in the lubricant oils. Further, the role of hygroscopic lubricant oil film of dispersed additives on the friction and wear reduction is schematically discussed.

Tribological Mechanism of Friction and Wear Reduction Using Oil-Based ZnO Nanofluid Applied on Brass

In this research, friction and wear characteristics of oil-based ZnO nanofluid applied on brass disk specimens using a flat-on-flat reciprocating sliding test were studied. Oleic acid was used as surfactant to improve the stability and dispersibility of the ZnO nanofluid. Metallurgical optical microscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy were utilized to understand the mechanisms. A 2wt% ZnO nanofluid resulted in 61.1% reduction in coefficient of friction. Good wear resistance was achieved using low concentrations of 0.5wt% and 1wt% ZnO nanofluid. A tribo-film mainly composed of carbon was found inside the wear track, which enhanced the wear resistance and lowered the interface shear strength. This tribo-film was produced by oleic acid which was chemically adsorbed to the brass materials.

The Effect of Agglomeration Reduction on the Tribological Behavior of WS2 and MoS2 Nanoparticle Additives in the Boundary Lubrication Regime

This study investigates the impact of different surfactants and dispersion techniques on the friction and wear behavior of WS2 and MoS2 nanoparticles additives in a Polyalphaolefin (PAO) base oil under boundary lubrication conditions. The nanoparticles were dispersed using Oleic acid (OA) and Polyvinylpyrrolidone (PVP) to investigate their impact on particle agglomeration. The size distribution of the dispersed nanoparticles in PAO was measured by dynamic light scattering. The nanoparticles treated using PVP resulted in the most stable particle size. Friction studies showed that nanoparticle agglomeration reduction and the homogeneity of the suspension did not significantly impact the friction reduction behavior of the lubricant. Reciprocating wear experiments showed that, for our test conditions, both WS2 and MoS2 nano additives exhibited maximum wear depth reduction (45%) when using the PVP surface treatment compared to base oil. The wear results confirmed the significance of minimizing agglomeration and promoting high dispersion in promoting favorable wear resistance under boundary lubricant conditions. Analysis of the wear surfaces showed that a tribofilm formation was the primary wear reduction mechanism for WS2 particles treated by PVP while, in the case of MoS2 treated by PVP, the mechanism was load sharing via particles rolling and/or sliding at the interface.

Microstructure and tribological properties of laser cladded self-lubricating nickel-base composite coatings containing nano-Cu and h-BN solid lubricants

In the present work, nickel-base composite powder (Ni60), nickel-base composite powder with the addition of h-BN solid lubricants (h-BN/Ni60) and nickel-base composite powder with the addition of nano-Cu encapsulated h-BN solid lubricants (nano-Cu/h-BN/Ni60) were used as raw materials to synthesize three different coatings on Q235 steels by laser cladding. Microstructures of these coatings were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. Tribological properties of these coatings were investigated at the temperatures from 25 °C to 600 °C. High temperature micro-hardness measurement was performed by Vickers micro-hardness tester. The results showed that the h-BN particles survived after laser cladding and displayed a homogeneous distribution in the nickel-base composite matrix. The encapsulation of h-BN by nano-Cu resulted in an increase of h-BN content in the coating. Although the addition of nano-Cu and h-BN led to a decrease on hardness, the nano-Cu/h-BN/Ni60 coating had the lowest friction coefficient and wear rate among the three coatings in a wide range of temperature from 25 °C to 500 °C. The mechanism of wear reduction by addition of nano-Cu encapsulated h-BN solid-lubricants was also discussed in this research.

Friction and wear reduction via tuning nanoparticle shape under low humidity conditions: A nonequilibrium molecular dynamics simulation

Because of the excellently thermal and chemical stabilities, nanoparticles have been considered as a potential lubricant additive to reduce friction and wear. In this study, nonequilibrium molecular dynamics simulations are used to reveal the friction and wear reduction mechanisms of diamond nanoparticle confined between the monocrystalline copper (Cu) slabs under low humidity conditions. The results indicate the movement pattern of nanoparticles can be changed from sliding to rolling by tuning the nanoparticle shape from a flat ellipsoid to a sphere. The sliding of sharp nanoparticles causes the water films being squeezed out from the worn region, which increases the surface friction and wear dominated by the polishing effect but impedes the formation of defects within Cu substrates. Contrarily, in the rolling process controlled by the rolling effect, a lot of water molecules remain in the worn region and thereby stop the surfaces from contacting with nanoparticles, which dramatically improves the friction and wear reduction. The interactive forces manifest the water films can transfer the normal force from slabs to nanoparticles during the rolling process. Therefore, by tuning the shape of nanoparticle additives to facilitate the rolling effect is helpful to reduce friction and wear in boundary or mixed lubrication.

Friction and Wear Reduction Mechanisms of the Reciprocating Contact Interfaces Using Nanolubricant Under Different Loads and Speeds

This study aims to reveal the roles and mechanisms of Al2O3/TiO2 hybrid nanoparticles into the lube oils which could reinforce engine components durability via reducing the friction, wear, or fuel economy in automotive engines. The tribological tests were carried out under different sliding speeds from 0.21 to 1.75 m/s and loads from 30 to 250 N using a reciprocating tribometer to simulate the ring/liner interface in the engine according to ASTM G181. The tribological results using hybrid nanolubricants suggested that the friction coefficient and wear rate of the ring decreased in the ranges 39–53% and 25–33%, respectively, compared to nanoparticles-free lube oil. The combined evidence of the worn surfaces analysis confirmed that the key mechanisms in antifriction and antiwear are a combination of the nanoparticles rolling mechanism and the replenishment mechanism of tribofilms on the sliding contact interfaces. In addition, a tribofilm formed on the rubbing surfaces is not only from the nanoparticles but also from Fe which is formed as a result of iron debris particles and oil additive package such as P and S originating from zinc dialkyldithiophosphate.

Experimental analysis of tribological properties of ultrasonically dispersed garnet nanoparticles in SN500 grade lubricating oil

PurposeThe optimal performance of the machinery is based on lubricants that require frequent monitoring and the analysis of characteristics such as chemical content, contamination and viscosity. The application of nanoparticles dispersed lubricant in tribology has received remarkable attention in recent years. This paper aims to investigate the tribological properties of SN500 grade lubricating oil containing garnet nanoparticles.Design/methodology/approachIn this study, 45-nm-sized garnet particles are ultrasonically dispersed in SN500 grade base lubricant oil. The effects of viscosity and additive concentration on tribological properties are investigated using a four-ball tester.FindingsRolling, reinforcing and film-forming behaviour of dispersed nano-sized garnet additives in the rubbing zone were investigated using scanning electron microscopy equipped with energy dispersive spectroscopy. The results indicate that the garnet additives can improve the wear resistance and resistance to relative motion and decrease the friction coefficient of rubbing steel interface by surface polishing and formation of tribo-film containing Si, C and Mn.Originality/valueBecause of the complex two-phase solid–liquid mixture, there are still limited physical understandings of the friction and wear reduction mechanisms. Therefore, the present research was undertaken to interpret the possible phenomena.

Friction and Wear Reduction Mechanism of Polyalkylene Glycol-Based Engine Oils

ABSTRACT Polyalkylene glycols (PAG) have been explored as a possible base stock for engine oil formulation. The friction, wear, and load-carrying capacity of five different PAG chemistries were evaluated either as a base stock or as formulated oils in pure sliding and sliding-rolling conditions using various laboratory bench test rigs operating under boundary and mixed lubrication regimes. The results were compared against GF-5 SAE 5W-20 and a mineral-based oil. The wear surfaces were also characterized using various surface-sensitive techniques for analysis of tribofilms to understand the mechanism of friction reduction. The results indicated that PAG oils show lower friction/traction coefficients and improved load-carrying capability, depending on the formulation, than those of the GF-5 SAE 5W-20 and mineral-based oil. The adsorption of PAG molecules on the surface appeared to be responsible for the lower friction characteristics.