Friction Modifiers Research Articles

Production of boric acid added brake friction composite and the effect of heat treatment on braking characterization

Purpose The purpose of this study was to investigate the use of boric acid as a friction modifier material in brake friction composites and to determine the effect of heat treatment applied during production on braking performance. Design/methodology/approach The addition of five different amounts of boric acid was balanced with cashew, which is in the friction modifier material group. The samples were produced in the following order: dry mixing, preforming and hot-pressing. The effect of the heat treatment that can be applied after the hot-pressing process on the braking performance was investigated. The tribological and physical properties of the samples were determined using tests performed according to appropriate standards. The microstructures of the friction surfaces were investigated using scanning electron microscopy. Findings It was observed that the tribological properties of brake friction composites containing 20% by weight of boric acid were improved. It has also been observed that the heat treatment applied after hot pressing increased the friction coefficient of the samples by 7% on average and decreased the specific wear ratio of the samples. When the surface morphologies of the samples are examined, it is seen that the friction layers of the heat-treated samples are wider, and the microvoids and cracks are reduced. Originality/value This study showed that boric acid can be used as a friction modifier in brake friction composites. It also revealed the tribological and physical contribution of the applied heat treatment to the composite. Thus, it guides brake friction composite manufacturers in the industry and researchers working in this field.

Revisiting Frictional Characteristics of Graphene: Effect of In-Plane Straining

Supreme mechanical performance and tribological properties render graphene a promising candidate as a surface friction modifier. Recently, it has been demonstrated that applying in-plane strain can effectively tune friction of suspended graphene in a reversible manner. However, since graphene is deposited on solid surfaces in most tribological applications, whether such operation will result in a similar modulation effect becomes a critical question to be answered. Herein, by depositing graphene onto a stretchable substrate, the frictional characteristics of supported graphene under a wide range of strain are examined with an in situ tensile loading platform. The experimental results show that friction of supported graphene decreases with increasing graphene strain, similar to the suspended system. However, depending on the adherence state of the graphene/substrate interface, the system exhibits two distinct friction regimes with significantly different strain dependences. Assisted by detailed atomic force microscopy imaging, we attribute the unique behavior to the transition between two friction modulation modes, i.e., contact-quality-dominated friction and puckering-dominated friction. This work provides a more comprehensive view of the influence of strain on surface friction of graphene, which is beneficial for active modulation of graphene friction through strain engineering.

An experimental study on the effects of friction modifiers on wheel–rail dynamic interactions with various angles of attack

By modifying friction to the desired level, the application of friction modifiers (FMs) has been considered as a promising emerging tool in the railway engineering for increasing braking/traction force in poor adhesion conditions and mitigating wheel/rail interface deterioration, energy consumption, vibration and noise. Understanding the effectiveness of FMs in wheel–rail dynamic interactions is crucial to their proper applications in practice, which has, however, not been well explained. This study experimentally investigates the effects of two types of top-of-rail FM, i.e. FM-A and FM-B, and their application dosages on wheel–rail dynamic interactions with a range of angles of attack (AoAs) using an innovative well-controlled V-track test rig. The tested FMs have been used to provide intermediate friction for wear and noise reduction. The effectiveness of the FMs is assessed in terms of the wheel–rail adhesion characteristics and friction rolling induced axle box acceleration (ABA). This study provides the following new insights into the study of FM: the applications of the tested FMs can both reduce the wheel–rail adhesion level and change the negative friction characteristic to positive; stick–slip can be generated in the V-Track and eliminated by FM-A but intensified by FM-B, depending on the dosage of the FMs applied; the negative friction characteristic is not a must for stick–slip; the increase in ABA with AoA is insignificant until stick–slip occurs and the ABA can thus be influenced by the applications of FM.

The effect of barite addition and graphite particle size on the specific abrasion of fly-ash/phenolic composite for brake lining application

Annually, million tons of fly-ash and bottom fly-ash is a waste of coal power plant. Fly ash contains Iron-oxide, alumina and silica. Those hard particle makes fly-ash can be used as a reinforcement in polymer composite. This composite is a wear resistance material and can be used as material for brake lining application. Fly ash reinforced phenolic composite has a low specific abrasion. The composite for brake lining material consisted of the reinforcement, friction modifier, solid lubricant and filler. Graphite is used as solid lubricant while barite is used as filler. Many research were carried out research on the particle size effect on the composite mechanical properties. However the size different between the constituent in composite has not investigated. Also the optimal barite weight fraction has not being observed. The composite was made by mixing all of the constituent, pressing in the mold and curing. The result show that the graphite particle size ? 150 mm has the lowest specific abrasion. The observation using scanning electron microscope shows that the composite contained small particle of ? 56 mm tends to agglomerate than the composite contained larger particle of ? 150 mm. the composite contained 15% barite has the lowest specific abrasion. The micrograph of scanning electron microscope shows the mixed of phenolic and barite evenly covered the graphite and fly-ash particles.

Green recycling of aramid fiber waste as the friction modifier of POM by solid state shear milling technology

AbstractAramid fiber is widely used in aerospace, machinery, construction, and other fields for its high strength, high elastic modulus, lightweight, and superior comprehensive performance. However, because aramid fiber is difficult to be melted and reprocessed, efficient and environmentally friendly recycling of aramid fiber waste (AFW) is an urgent and challenging issue. In this work, we reported a facile way to recycle AFW for the preparation of friction‐resistant polyoxymethylene (POM)/AFW composites. The ultrafine AFW powder with 64.69 μm in size was fabricated by solid state shear milling (S3M) technology, which broke the amide bond due to the strong compression and shearing during milling. With the increase of milling cycles, the roughness and active groups on the surface of AFW were increased, which was contributed to improving the compatibility between AFW and POM matrix. The morphology observation indicated a good dispersion of AFW in POM. The mechanical property test results showed that the flexural strength increased from 52.69 MPa to 80.12 MPa with 20 wt.% AFW. As a friction modifier, the addition of AFW could improve the tribological properties of POM/AFW composites, and the coefficient of friction (COF) and wear rate of composites with 20 wt.% AFW could decrease by 53.02% and 69.52%, respectively. The S3M technology presented in this work is an efficient and industrialized strategy for AFW recycling to prepare value‐added products, which has great potential in the engineering application field.

Combining micro-infrared reflection absorption spectroscopy with density functional theory for investigating the adsorption of organic friction modifiers on steel surfaces

Friction plays a major role in contributing to the global energy consumptions and reducing it would bring about major economic and environmental advantages. Organic friction modifiers are cost-effective and environmentally friendly additives which are included in the lubricant packages to improve performances. Their friction-reducing properties are connected to their adsorption state on steel surfaces. This study applies Infrared Reflection Absorption Spectroscopy (IRRAS) to probe the oleic acid tribofilm on microscopic areas of the sample (micro-IRRAS). The recorded spectra are interpreted by density functional theory (DFT) calculations and provide useful information about the effect of the tribological phenomena on the adsorption state and molecular orientation of the oleic acid friction modifier. The oleic acid molecules adsorb on the surface forming both monodentate and bridging configurations on the iron atoms. IRRAS data show that under the effect of friction the molecules tilt towards the steel surface.

Lubrication mechanism of a strong tribofilm by imidazolium ionic liquid

Friction modifiers (FMs) are surface-active additives added to base fluids to reduce friction between rubbing surfaces. Their effectiveness depends on their interactions with rubbing surfaces and may be mitigated by the choice of the base fluid. In this work, the performance of an imidazolium ionic liquid (ImIL) additive in polyethylene-glycol (PEG) and 1,4-butanediol for lubricating steel/steel and diamond-like-carbon/diamond-like carbon (DLC—DLC) contacts were investigated. ImIL-containing PEG reduces friction more effectively in steel—steel than DLC—DLC contacts. In contrast, adding ImIL in 1,4-butanediol results in an increase in friction in steel—steel contacts. Results from the Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and focused ion beam-transmission electron microscopy (FIB-TEM) reveal that a surface film is formed on steel during rubbing in ImIL-containing PEG. This film consists of two layers. The top layer is composed of amorphous carbon and are easily removed during rubbing. The bottom layer, which contains iron oxide and nitride compound, adheres strongly on the steel surface. This film maintains its effectiveness in a steel—steel contact even after ImIL additives are depleted. Such film is not observed in 1,4-butanediol where the adsorption of ImIL is hindered, as suggested by the quartz crystal microbalance (QCM) measurements. No benefit is observed when the base fluid on its own is sufficiently lubricious, as in the case of DLC surfaces.This work provides fundamental insights on how compatibilities among base fluid, FM, and rubbing surface affect the performance of IL as surface active additives. It reveals the structure of an ionic liquid (IL) surface film, which is effective and durable. The knowledge is useful for guiding future IL additive development.

Rheological and tribological evaluation of friction modifiers for wheel‐rail applications

AbstractFriction modifiers (FM's) are substances deliberately applied to the top‐of‐the‐rail in the field in order to control the traction coefficient. In this work, two FM's, a commercial (FM1) and a custom‐made (FM2), and a gauge lubricant (CGL) were evaluated in the laboratory using rheological and tribological tests. Two rheological tests were done: oscillatory (frequency and strain sweeps) and flow tests (viscosity vs. shear rate). Tribological tests were done in a twin disk machine to obtain the traction coefficient under different slip values. Retentivity tests were also done in the same machine. Several physical–chemical tests were also done to characterise the products. The results of rheological tests showed that there are notable differences that can influence the performance of FMs. From the studied materials, the FM2 product tends to be more viscous even for high‐shear rates. The tribological tests showed that the traction coefficient is different for all the studied materials and changes from 0.15 to 0.45 depending on the creepage. The retentivity of FM2 is 1.9 times higher than FM1. The results show a good correlation between the rheological behaviour and the coefficient of traction and retentivity.

Effect of Molecular Weight on Tribological Properties of Polyether Amine Derivatives under Different Contact Modes

The requirements for the fuel economy of modern industry continue to drive the progress of low-viscosity lubricants. The present work reports the application of polyether amine derivatives as friction modifiers to improve the tribological properties of low viscosity poly-alpha-olefin. Three polyether amine derivatives with different molecular weights were synthesized, the tribological properties of which were systematically investigated under three different contact modes. These functionalized polymers exhibited significant friction reduction and wear resistance properties in the point-on-flat and line-on-flat friction tests, but just showed anti-wear performance in the severe point-to-point contact mode. The results exhibited that molecular weights of the polymers had a direct effect on their tribological properties. The increase of molecular weight in a certain range was beneficial to the improvement of tribological properties, but further undue increase will rather reduce the friction reduction and wear resistance performances. It can be indicated that the number of oxygen atoms increased with the molecular weight of the polymer, which will be conductive to the adsorption of the polymer on the metal surface. However, when the molecular weight of the polymer exceeds a certain value, the steric hindrance of the molecules adsorbing to the metal surface increases, which in turn has a negative impact on the tribological properties.

Molecules with a TEMPO-based head group as high-performance organic friction modifiers

High-performance organic friction modifiers (OFMs) added to lubricating oils are crucial for reducing energy loss and carbon footprint. To establish a new class of OFMs, we measured the friction and wear properties of N-(2,2,6,6-tetramethyl-1-oxyl-4-piperidinyl)dodecaneamide referred to as C12Amide-TEMPO. The effect of its head group chemistry, which is characterized by a rigid six-membered ring sandwiched by an amide group and a terminal free oxygen radical, was also investigated with both experiments and quantum mechanical (QM) calculations. The measurement results show that C12Amide-TEMPO outperforms the conventional OFMs of glyceryl monooleate (GMO) and stearic acid, particularly for load-carrying capacity, wear reduction, and stability of friction over time. The friction and wear reduction effect of C12Amide-TEMPO is also greatly superior to those of C12Ester-TEMPO and C12Amino-TEMPO, in which ester and amino groups replace the amide group, highlighting the critical role of the amide group. The QM calculation results suggest that, in contrast to C12Ester-TEMPO, C12Amino-TEMPO, and the conventional OFMs of GMO and stearic acid, C12Amide-TEMPO can form effective boundary films on iron oxide surfaces with a unique double-layer structure: a strong surface adsorption layer owing to the chemical interactions of the amide oxygen and free radical with iron oxide surfaces, and an upper layer owing to the interlayer hydrogen-bonding between the amide hydrogen and free radical or between the amide hydrogen and oxygen. Moreover, the intralayer hydrogen-bonding in each of the two layers is also possible. We suggest that in addition to strong surface adsorption, the interlayer and intralayer hydrogen-bonding also increases the strength of the boundary films by enhancing the cohesion strength, thereby resulting in the high tribological performance of C12Amide-TEMPO. The findings in this study are expected to provide new hints for the optimal molecular design of OFMs.

Thermal Friction Characteristics of Engine Elements - Boundary Lubrication of Cam and Tappet

As low-viscosity oil is used more widely to reduce friction losses in IC engines, concerns are growing about an increase in friction, wear and scuffing at the sliding surfaces on tribo-components. The authors conducted an analytical study on thermal friction characteristics of boundary lubrication based on the physical and chemical properties of interface materials and lubricants. The study was intended to investigate the effect of temperature on the function of oil additives as a friction modifier and/or anti-scuffing agent. Three low viscosity base oils, three extreme pressure and anti-wear agents and two organo-molybdenum friction modifiers were used to measure friction changes with a cam/follower test apparatus. The authors analyzed a relationship between friction and temperature in the running-in process of interfaces in consideration of the functional sensitivity of additives in low-viscosity oils. This analysis was focused on physicochemical properties on the basis that the oil viscosity, the adsorption of oil molecules, the chemical reaction of oil additives that forms a tribo-film low in shear stress, and the strength of interface materials are all under the influence of the exponential function of temperature, just like the Arrhenius’ equation. The results of the analysis found that the frictional shear stress changes depending on the intensity of involvement of surface temperature that affects oil viscosity, molecular adsorption / desorption and tribo-film formation in each running-in term.

Low friction tribofilm formation and distribution on an engine cylinder tested with MoDTC-containing low viscosity engine lubricants

The piston-liner tribological contact has a key role in controlling friction caused energy losses in a passenger car engine. This study analyses the MoDTC-containing low viscosity lubricant performance and the resulting low-friction MoS2 tribofilm distribution on the liner surface. The engine liners were tested in a floating liner measurement system, where fully-formulated lubricants with different MoDTC concentrations were utilised to assess the impact of friction modifiers on the friction performance. Tested engine liners were dismantled from the measurement system, and MoS2 tribofilm formation on the liner was quantitatively characterised by Raman Microscopy mapping. The MoS2 tribofilm chemical composition and lamellar structure were further investigated by Transmission Electron Microscopy (TEM), High-Angle Annular Dark-Field Scanning (HAADF) and Energy Dispersive X-ray (STEM-EDX) Microscopy. The findings presented in this paper confirm that MoS2 tribofilm spatial distribution plays a pivotal role in reducing friction in piston-liner contact. 60% friction torque reduction was achieved at BDC area with 0.7% MoDTC concentration in the fully formulated lubricant. Moreover, MoS2 presence in the middle of the liner indicates MoDTC effectiveness throughout the whole engine cycle. Therefore, contributing to the overall energy savings in passenger cars.

Carrydown of liquid friction modifier

A small-scale laboratory apparatus was built to study liquid friction modifier (LFM) behavior in a top-of-rail application. A field experiment was also carried out to complement the laboratory findings. KELTRACK® (a water-based LFM) was used as the test fluid. Laser-induced fluorescence served to measure the LFM thickness left on the track after the passage of the wheel. The lab experiments show that the LFM cannot withstand the high wheel-rail contact pressure in the nip present in cargo rail situations. As a result, the liquid is squeezed out laterally and attaches to the edges of the wheel contact band. This “edge liquid” is then carried down the track on the wheel. Gravimetric measurements of the wheel contact band confirm this observation, and show that only a minute amount of liquid is carried through the nip in the valleys between surface roughness features. In the field experiment, the LFM is applied from a trackside unit on a tangent section of the track. About 500 m downstream of the application point, the track has a curved section. LFM cannot be detected anywhere on the track a short distance (∼200 m) past the application unit. However, LFM is detectable on the curved sections of the track up to approximately 2 km from the application unit. This LFM on the curved track is believed to be due to transfer of the “edge liquid” from the wheel to the track, caused by the movement of the contact band as the train rounds a curve. The presence of LFM on the curved track far downstream is consistent with prior measurements of reduced lateral force on the curved track downstream of LFM application sites.

Numerical prediction on the effect of friction modifiers on adhesion behaviours in the wheel-rail starved EHL contact

Previous third body studies for wheel/rail are mainly concentrated on water or oil condition. However, friction modifiers (FMs) represent a new approach to managing adhesion coefficient in wheel/rail interface. In this paper, the position of the FM-air meniscus was given as input parameter, the thickness of FM can be solved easily with the multi-grid method. Non-Newtonian fluid model and micro-EHL analysis combined to obtain the relation between the adhesion coefficient and the quantity of FM. The results show that the quantity of FM has a significant effect on the initial adhesion coefficient within a certain range. Besides, the initial adhesion coefficient decreases gradually until it reach stable value with the increase of the quantity of FM.

Adsorption Behavior of TEMPO-Based Organic Friction Modifiers during Sliding between Iron Oxide Surfaces: A Molecular Dynamics Study.

Organic friction modifiers (OFMs) added to lubricating oils to reduce friction and wear are crucial for reducing energy loss and CO2 emissions. In our previous studies, we have developed N-(2,2,6,6-tetramethyl-1-oxyl-4-piperidinyl)dodecaneamide, referred to as C12TEMPO, as a new type of OFM and experimentally demonstrated its superior performance to conventional OFMs of stearic acid and glycerol monooleate. However, the behavior of C12TEMPO adsorbing onto solid surfaces from base oil during sliding, which largely dictates the lubrication performance, is yet to be elucidated. Here, we performed molecular dynamics simulations for confined shear of a C12TEMPO solution in poly-α-olefin between hematite surfaces. Unlike conventional OFMs, which typically have one functional group or multiple functional groups of the same type, C12TEMPO features two functional groups of different types: one amide and one terminal free oxygen radical. The results showed that adsorbed boundary films with a double-layer structure form stably during sliding, owing to double- or single-site surface adsorption and interlayer hydrogen bonding via the two functional groups. Additionally, some molecules in each of the first and second layers also form intralayer hydrogen bonding. Such multitype adsorption is unique and favorable for enhancing the strength of boundary films to withstand heavily loaded and prolonged sliding. The velocity distribution indicates that the first and second layers are solid- and liquid-like, respectively. The second layer could act as a buffer for the first layer, which is the last barrier to prevent solid-solid contact, against shear. We also found that the second layer can act as a reservoir to rapidly repair the once depleted region in the first layer because of the interlayer hydrogen bonding. The combination of the high strength and self-repair ability of the C12TEMPO boundary films can rationally explain the experimentally observed properties of high load-carrying capacity, excellent antiwear effect, and high stability of friction over time.

Ultrafine fully vulcanized natural rubber modified by graft-copolymerization with syrene and acrylonitrile monomers

Natural rubber (NR) is known as one of the most important renewable agricultural resources in Thailand. To enhance the NR's value, development and utilization of NR in form of commercial product are necessary. Commercial product based on ultrafine fully vulcanized powdered rubber (UFPR) was widely used in numerous potential applications such as toughening filler or friction modifier in brake pads. However, to meet the required thermal stability of friction modifier in brake pads for replacing the synthetic rubber powder, the modification of NR by graft-copolymerization with styrene (ST) and acrylonitrile (AN) monomer and production into the powder form are promised related to a sustainable economic system. From the beginning, the grafting process of NR latex was prepared by emulsion graft-copolymerization with ST and AN monomers onto deproteinized natural rubber (DPNR). The results revealed that the grafting with ST/AN monomer content of 80/20 weight ratio possessed the monomer conversion and grafting efficiency as high as 71% and 63%, respectively. After that, the obtained DPNR-g-(PS-co-PAN) was radiated by an electron beam, followed by a spray drying process to produce ultrafine fully vulcanized powdered natural rubber (UFPNR-g-(PS-co-PAN)). The SEM micrographs showed that UFPNR particles are relatively spherical with a particle size of approximately 3.56 μm. Furthermore, thermal stability i.e., degradation temperature at 5 % weight loss (Td5) of the modified UFPNR was substantially improved from 334 to 350°C. The benefits of these advanced technologies give an obvious conclusion proved that the modified UFPNR is a good candidate for replacing a commercial synthetic powdered rubber and suitable for using as toughening filler in high performance polymer composite applications.

Экспериментальное исследование трибологических характеристик смазочных масел со слоистыми модификаторами трения и возможности их применения в судовой технике

The paper presents the results of studying the lubricity of several lubricating compositions, two of which contain an antiwear additive based on a layered friction modifier - molybdenum diselenide. Oil MC-20, which does not contain functional antiwear additives, is used as a base lubricating medium and an object of comparison. Two variants for combining an antiwear additive with this oil differ in the process of initial preparation of the additive before adding it to the base lubricating oil by rotary pulsation grinding and stirring. Antiwear tests are arranged in the form of a consistent tribological rating of the given types of lubricating media at various operating time of the friction path of the test samples. The test tool is a rotary-type friction machine of an original design. There are analyzed the differences in the antiwear test methodology and the advantages of the proposed scheme over the analogous one, which is relevant for GOST R 51860-2002. Among the results of the tribological study carried out, topographic patterns of wear of test specimens, the dependence of the wear rate of tribological surfaces on contact pressures, and the dependence of the wear scar diameter on the amount of specimen wear are given. The antiwear additive has been found to contain a layered friction modifier of selenium dichalcogenide (molybdenum diselenide) type, it improves the lubricating film on friction surfaces and reduces their wear compared to the use of nonadditive oil MS-20. The wear degree of a stationary ball-shaped specimen when testing a lubricating medium with the antiwear additive is reduced by 66-85% compared to a base lubricating oil without additives. The diameter of the wear spot on a stationary specimen under these test conditions is reduced by 28-67%, which proves the effectiveness of preliminary preparation by rotary-pulsation mixing of a lubricant composition with a solid suspended base even with a relatively short preparation time.

Trimethylolpropane trioleate as eco-friendly lubricant additive

Approximately 17.9% of fuel energy is used to overcome engine friction in passenger cars with engine frictional losses further broken down into losses along hydrodynamic (40%), elastohydrodynamic – due to pure sliding motion (40%), mixed (10%) and boundary (10%) lubrication regimes. Therefore, to assess the tribological influence of TMP trioleate as an eco-friendly additive to a low viscosity Polyalphaolefin (PAO) at different lubrication regimes, the present study adopted a Stribeck-type analysis. Through this study, the viscosity index of PAO was found to increase significantly when blended with 5-vol% TMP trioleate. Tribologically, across the tested conditions at different sliding velocities and applied normal loads, it was determined that this blend could potentially reduce friction power and wear scar diameter by up to 6.09% and 39.65%, respectively, when compared with the neat PAO. Such an improvement was demonstrated to also synergistically enhance the friction modifier effect of this blend at the mixed lubrication regime, delaying the onset of boundary lubrication regime when the contact is lubricated by this mixture.

Effect of Steel Hardness and Composition on the Boundary Lubricating Behavior of Low-Viscosity PAO Formulated with Dodecanoic Acid and Ionic Liquid Additives.

Two ionic liquids, tributylmethylphosphonium dimethylphosphate (PP) and 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate (BMP), as lubricant additives in polyalphaolefin (PAO8) were studied under boundary lubricating conditions on two types of steel (AISI 52100 bearing steel and AISI 316L stainless steel). The tribological behavior of these ILs was compared with dodecanoic acid, a well-known organic friction modifier. This study employs a ball-on-disk tribometer with an alumina ball as a counterpart. A range of advanced analytical tools are used to analyze the tribofilms, including scanning electron microscopy equipped with a focused ion beam, scanning transmission electron microscopy equipped with X-ray energy-dispersive spectroscopy, and X-ray photoelectron spectroscopy. A quartz crystal microbalance with dissipation was used to study the surface adsorption of the additives on iron- and stainless steel-coated sensors to reveal the adsorption kinetics, adsorbed layer mass, and bonding strength of the adsorbed layer on the metallic surfaces. The most important factors controlling friction and wear are the thickness and viscoelastic properties of the adsorbed layer, the thickness and chemical composition of the tribofilm, and the hardness and chemical composition of steel. Among all additives studied, BMP on stainless steel gives a strongly adsorbed layer and a durable tribofilm, resulting in low friction and excellent antiwear properties.

Effect of Nickel Silicide Content on the Friction Properties of Wet Sintered Friction Material

The effect of nickel silicide on the friction properties of Cu-based wet sintered friction materials was investigated. The microstructure and mechanical properties of nickel silicide added Cu-based wet sintered friction materials were examined. Nickel silicide was prepared by mechanically alloying Ni and Si powder. Three types of Cu-based wet sintered friction materials with different nickel silicide contents (0 wt%, 5 wt%, 10 wt%) were fabricated by the powder metallurgy route. The phase transformation of Ni2Si to Ni31Si12 was observed in nickel silicide after a sintering process. The friction coefficient and wear rate decreased with increasing nickel silicide content. The wear scar changed from ploughing to micro-cutting with increasing nickel silicide content. As a result, it is suggested that nickel silicide can be used as a friction modifier when added to Cu-based wet sintered friction materials.