GB2529384A

GB2529384A - A plain bearing with composite interplayer

Info

Publication number: GB2529384A
Application number: GB1411143.9A
Authority: GB
Inventors: Yi Zhang; Madan Pal; Grazina Burmistroviene; Ian Kerr; Ignacio Tudela Montes; Andrew Joseph Cobley; Timothy James Mason
Original assignee: Daido Metal Co Ltd
Current assignee: Daido Metal Co Ltd
Priority date: 2014-06-23
Filing date: 2014-06-23
Publication date: 2016-02-24
Also published as: GB201411143D0

Abstract

This invention relates to a method of applying a coating layer 90 to a bearing substrate 93 which contains a matrix of particles 91 within the coating. The particules 91 are contained within an electrolytic solution along with the surface to be coated 93. Electoplating is used to deposit the metal ions 92 as well as the hard or soft tribologically useful particulates 91 onto the surface 93. Ultrasonic or megasonic agitation is used to scatter and disperse the particles 91 within the electrolytic solution to ensure a uniform concentration of particles 91 near the surface 93 of the part.

Description

A plain bearing with composite interlayer

DESCRIPTION

This invention relates to a coating with embedded particles and refined microstructure for use as interlayer in plain bearings in order to improve bearing S performance and reliability, and a process to produce such coatings.

In internal combustion engines, plain bearings are used as main-bearings to support a crankshaft in engine crankcase and big-end bearings to connect connecting-rods with the crankshaft. The bearing bears the load from the combustion process and inertial loads form the rotation of crankshaft. In modern engines, the bearing specific loads and the intensity of fatigue loads are increasing as more and more power is obtained from the ever smaller and lighter engines. There is also a trend to use thinner viscosity lubricants to achieve more efficiency by reducing parasitic losses from engine components. The use of low viscosity lubricants reduces the minimum oil film thickness causing bearings to run in mixed and boundary lubrication regime and combining this with other factors such as engine downsizing leads into bearings operating under arduous conditions. Generally, for such applications, bearings with low friction and good anti-seizure properties are desirable.

A plain bearing used in highly loaded engines is made of at least three or more layers of alloy/composite materials, commonly known as tn-metal bearing. The plain bearing has a steel backing to give strength to the bearing, allowing a proper interference fit in the housing. The steel backing is coated with a copper or aluminium based lining material by casting, sintening, roll bonding, or other methods. Lining materials have good load capacity, wear resistance and cavitation resistance, but may lack the necessary compatibility, conformability and embeddability, to operate satisfactorily.

To accommodate this, a soft overlay may be coated over the bearing lining to give the necessary low frict.iori, cornpatihüity, contormabiiit.y and embE.ddabUity. Often an interlayer is* requ Wed between the ove!lay d the ining to serve as a bondng iayr and/or to act as a diffusion harrier, In tri.metai bearings with bronze linings the overlay generally contains elements such as Sn, among other metals that may diffuse into the bronze lining. In this case a few micron thick Ni coating is commonly used as an interlayer between the overlay and the bronze lining, Without the Ni intenlayer Sn from the overlay and from the bronze lining may migrate towards the bonc,flng interface therehetween at norma engine operating temperatures. There is ther&ore a dak of forming hard and brittle ir.termetahc compounas such CuSn. Furthermore, the depleton of Sn and/or Cu from the overlay and the formation of the intermetallic compounds will lead to a reduction in fatigue strength, corrosion, wear and seizure performance. Essentially a Ni interlayer between the overlay and lining is designed to control and limit diffusion.

In tn-metal bearings with aluminium linings a few micron thick Ni coating is often used as an interlayer between the overlay and the aluminium lining. The Ni layer acts to improve adhesion between the aluminium lining and the soft metal overlay.

If the Ni interlayer is exposed to the running shaft during operation by wear, corrosion or other mechanisms it may lead to the seizure of a bearing due to the poor tribological performance of Ni against steel shafts. In such cases, an intertayer with good tribological properties would be highly desirable.

The deposition of Ni interlayer coatings in plain bearings is well known.

Conventionally electroplated Ni interlayer from Watts electrolytes has a large and columnar grain structure (see Figure 2). Such Ni interlayer coatings present poor tribological properties, causing a poor bearing performance when the overlay is removed locally from the bearing surface and the Ni interlayer is exposed. A more refined structure can be achieved in the Ni interlayer electroplated from Watts electrolytes when the process is carried out under the presence of ultrasound/megasound (Figure 3).

As will be clear from the following detailed review of the existing prior-art there are many techniques which can be used for depositing Ni composite coatings. Most of these deposition techniques are unable to provide a finer grain structure for the Ni matrix but these processes are inefficient, ineffective, or too expensive for use in mass production.

US2008302668 describes a composite electroplating coating to produce a matt surface effect with Cu, Ni or Cu-Sn matrix and PTFE particles. A surfactant/wetting agent. a polyaikyiene oxide substituted q uaternary ammonium compound, is used to disperse PTFE oartctes of sb.e 10 to i000nm and 0.1 h.:1 000 mg/L quantity n the electroplatinq bath., altnoughno specific embodment of a partice size is disciosed., The surfactant forms a micro-emulsion andlor dispersion of PTFE in the electroplating bath which is then plated as a composite coating to a metallic substrate. The addition of surfactants facilitates particle de-agglomeration, as it reduces the interfacia! tension between the liquid and the solid particles. However, the use of surfactants to disperse particles in electroplating bath have many disadvntarws, as the effective concentration of the surfactant required to have an 33 improvement in particle dispersion may provoke undesired effects on the pcoperlies n *1 of the electrodeposited coatings. In addition, it makes the production process difficult to control and reduces the life of the electroplating bath.

GB953506 describes a wear resistant Ni composite coating with mica dispersed in the Ni matrix. The coating is deposited from an electroplating bath and to disperse S mica particles in the coating matrix the electroplating bath is agitated by rotating the cathode during plating. The disadvantage of such an agitation process is that it does not prevent particle agglomeration in the electrolyte, the dispersion of the particles in the coating is uneven and the microstructure is not refined.

US200S1 9662 describes a wear and friction reducing Ni composite coating with PTFE. molybdenum disulphide. hexagonal boron nitride, tin sulphide, graphite and other particles dispersed in the Ni matrix. The coating is deposited from an electroless plating solution. However, there are many disadvantages associated with using electroless plating to deposit composite coatings. The electroless plating technique relays on reducing agents which make the plating solution complex and difficult to control. Electroless Ni must be carried out at high temperatures requiring a high amount of energy to plate the coating. The lifespan of chemicals used in the electroless plating process is limited, the deposition rates are low, and effluent treatment is expensive. These factors increase the operational costs.

Electroplating processes using surfactants, gas or mechanical agitation to disperse particles in a Ni-based composite coating give no improvement in Ni microstructure and/or particle dispersion/agglomeration in both the electrolyte and the coating. Such processes are difficult to control in production. These same disadvantages are applicable to the deposition of composite coatings using electroless plating techniques 23 DE102010011083 describes an electroless plated Ni composite coating containing 5 to 30 % by weight o tnbologcal paftcies such as graphfle, molybdenum disuohide, &xagonal boron itride or FFE. DEl 02011513881 desobbes a coating corn posito ocabng deposded by &octroiess pahng made o Nb, Cu. A or Co contanig Sin 30 % by volume of trihologicai particles such as graphite. molybdenum thsupMide, $0 hexagonal boron ntride and/or PTFE to improve the ow friction and hthrication properties of the coating and ito 15 % by volume of tribologically active particles such as carbides, cubic nitrides. oxides and/or silicides to improve the abrasion and wear resistance of the coating. These composite coatings are used as a 3 to 12pm thick interiayer in riain hearings, As such coatings are poduced from an elec,irotess process and no specific dispersing method is mentioned, they suffer from the disadvantages discussed earlier.

The journal article "Co-deposition of inorganic fullerene-like WS2 nanoparticles in an electrodeposited nickel matrix under the influence of ultrasonic agitation" Electrochimica Acta 114 (2013) 859-867, discloses Nickel layers containing IF-WS2 particles produced using ultrasound in the deposition process.

Electroplating processes using surfactants, gas or mechanical agitation to attempt to disperse particles in a metal based composite coating do not prevent particle agglomeration in the electrolyte or in the coating itself These processes are difficult to control in production and are inefficient, ineffective, or too expensive for use in mass production. The same disadvantages apply to the deposition of composite coatings using electroless plating techniques. It is amongst the objects of the invention to address one or more of the above problems.

In the present invention, the inventors have sought a solution to the continuing problem of providing an even dispersion of particles in composite coatings and refining the microstructure of interlayer coatings so that effective muftifunctional diffusion interlayers with enhanced tribological properties are achieved. The inventors have independently and successfully developed techniques to produce composite coatings with an even dispersion of particles with finer and improved grain structure.

Such even dispersion of particles and grain refinement of the coating matrix is achieved by using different agitation techniques, i.e. ultrasound/megasound or a combination of ultrasonic/megasonic and other agitation methods. In the case of using highly hydrophobic particles that are difficult to wet (and therefore the use of surfactants is required) the use of ultrasound/megasound or a combination of ultrasonic/megasonic with other agitation methods significantly improves the dispersion of particles with very liWe addition of the surfactant. reducing the oncentrahorA of the *s& ac;tant req'ured to wet the particles. and therefore minimizing the thsadvantages associated to their use. The composite coatings wth even dspersed partkJes and finer grain structure rirovide an, effective multifunctonal :30 interlayer with enhanced tribological and mechanical performance and superior reHability in local areas of the surface of plain bearings when the bearing is worn and the overlay has partially been removed during operation.

According to the present invention, there are provided composite coatings to be used as interlayers in plain hearings, with evenly dispersed particles in the coating, These coatings have a finer grain structure (see Figure 4 for more details).

In a general aspect the present invention provides a method of preparing a layer deposited on a substrate, comprising; i) providing an electrolyte bath which comprises metal ions and tribological particles, the bath having electrodes disposed therein, U) applying ultrasound or megasound to the electrolyte bath to disperse the particles, and iii) applying a potential difference between the electrodes to effect deposition of a composite of a metal layer having the tribological particles dispersed therein onto one of the electrodes, and wherein the electrode onto which the layer is deposited comprises the substrate.

The tribological particles are preferably comprise one or more types of a soft material having a Mohs hardness of «= 5, as will be described in more detail below.

So the composite coating consists of a matrix made of one metal or metal alloy with fine grain structure and particles uniformly dispersed in the metal matrix. The particles preferably consist of either one or more types of soft particles with Mohs hardness «= 5, but could alternatively consist of one of more types of hard particles with Mohs hardness> 5. (most preferably >5.5) or a combination of one or more types of both soft and hard particles.

The metal coating is deposited from an electroplating bath in which the soft and/or hard particles are dispersed by using ultrasonic/megasonic or a combination of ultrasonic/megasonic and other agitation techniques. The use of ultrasound/megasound not only uniformly disperses the particles in the composite coating but also refines and modifies the grain structure of the coating.

The applicatior of ultrasound or megasound, either before or during the &ethodeposition process provides a deposited ayer with a metal matnx f/hioh has a more refined grain structure than layers produced in the absence of ultraso',iflC or riegasound The comparison between the grain structures oroduced with and without ultrasound is shown in figures 24. Furthermore, the spatial dispersion of the tribological particles within the matrix is more uniform. It is thought that both of these factors provide a layer with improved tribological properties, for example a lower coefficient of friction. Bearings containing such a layer, for example as an interlayer, are therefore less prone to seizure The hearings may also he more efficent due to reduced fnctionai iosses.

The process is more efficient than prior art deposition methods because the ultrasound or megasound disperses the tribological particles in the bath. This prevents the particles from clumping in the bath. In some electroplating processes it is usual to add a surfactant to the bath to prevent particle clumping. This may be done when using highly hydrophobic tribological particles that are difficult to wet. The application of ultrasound or megasound enables the use of less surfactant. This is advantageous because the disposal of surfactants is inconvenient.

The prevention of clumping in the bath also gives rise to a deposited layer with an improved size distribution of tribological particle sizes. This is shown in figures 5-7.

The range of diameters of the dispersed particles is narrower in those layers prepared using ultrasound or megasound irradiation, than in those prepared without ultrasound or megasound. The improved size distribution provides a layer with improved tribological properties, for example a low coefficient of friction.

The coating has a thickness of 0.1 to lSpm, preferably 0.5 to 8pm, typical tribological coatings as per the invention are preferably 0.510 5pm thick.

The metal matrix of the coating consists of a metal selected from the group Ni, Cu, Cr, Go, Fe or alloys based upon any of these metals.

The soft particles dispersed in the composite coating may be one or more materials selected from a group of tribological materials/solid lubricants such as PTFE, fluorinated polymers, metal sulphides, metal fluorides, metal suiphates, graphite and other soft carbonaceous particles, hexagonal boron nitride (hBN), phyllositicates, zinc oxide or lead oxide.. The hard particles dispersed in the composite coating may be one or more of a group of metal oxides, borides, carbides, nitrides, silicides, diamond. carbon nanotubes, graphene and other hard carbonaceous particles. Both lubricant and hard particles have a nominal size of mm to 10pm. preferably 2SOnrn to 2.pm.

The:oatirq may be deposited on a variety of substrates includng. but no irnited to.

bronze, hrss, white rnetai, aluminum alloys, stee and other bearing materials.

The substrate may be conficured as a portion of a plain bearing and the coating is applied to form an interlayer coating. For example, the substrate may be a bearing half shelL Thus, the method of the invention may further comprise coating bearing surfaces of two bearing half shells, which are then assembled into a housing to form a complete pfrain oumai heanng.

Thus in one aspect of the invention there is provided a method of forming a plain bearing comprising: providing a backing substrate, with a bearing lining material deposited on the backing substrate, depositing an interlayer over the bearing lining material and depositing an overlay over the interlayer, wherein the interlayer is applied on the lining material by electroplating from a deposition bath in which tribologically useful particles are dispersed before and/or during electrodeposition of the interlayer by ultrasonic or megasonic agitation, or a combination of ultrasonic and megasonic agitation, and wherein the interlayer is thereby deposited as a composite of a metal matrix with a dispersion of said particles distributed therein.

The ultrasonic and/or megasonic agitation is preferably applied to the particles before electrodeposition commences and optionally also during electrodeposition.

The deposition bath is preferably agitated by a further agitation method such as stirring, which may be conducted before electrodeposition and/or during electrodeposition.

The ultrasonic and/or megasonic frequency may be between 10 and 3000 kHz, preferably from 15 to 200 kHz. The ultrasonic and/or megasonic power may be between 0.00001 and 50 W/cm3, preferably from 0.0001 to 5 W/cm3.

The ultrasonic and/or megasonic agitation and any other agitation methods may be applied before and/or during electrodeposition for a period of time longer than 0.01 seconds and no longer than 60 days, preferably between 20 seconds and 48 hours.

The ultrasonic and/or megasonic agitation and any other agitation methods are typically applied before and/or during electrodeposition for a period of time between 1 minute and 24 hours, preferably between 5 minutes and 4 hours.

The ultrasonic and/or megasonic agitation and any other agitation methods may be appUed as a genes of culs.es, The flme on during one pulse may range between 0.0501 seconas to 24 days ana the tme OtT durgcne puftAe may range L)etwan o oooi secc:nds. to 24 clays. Preferably the t*me our Imug one pwss ranges between. 0 001 seconds to 2 hours, and the tme off during one pulse ranges between 0.001 seconds to 2 hours The particles may comprise soft particles with Mohs hardness s 5.Alternatively the particles may comprise hard particles with Mohs hardness> 5. preferably »=5.5.

another embodiment the particles may comprise a combination of both soft (Mobs hardness S 5) and ha.rd (Mobs hardness 5, preferahy »=5 5*t parUces.

S

The particles deposited may be of a uniform composition, or the particles deposited may comprise two or more sets of particles having different compositions.

Preferably at least 95% of the tribological particles in the electrodeposition bath have diameters of 1 nm to 10 pm, preferably 250 nm to 2 pm, and most preferably 600 nm to2pm.

The interlayer metal matrix deposited by electroplating may comprise a metal selected from Ni, Cu, Cr, Ca, Fe or alloys based upon any of these metals.

In yet another aspect of the invention there is provided a plain bearing comprising: a backing substrate, a bearing lining material deposited on the backing substrate, an interlayer deposited over the bearing lining material and an overlay deposited over the interlayer, wherein the interlayer is deposited as a composite of a metal matrix with a dispersion of tribologically useful said particles distributed therein, preferably by a method as hereinbefore described.

The interlayer (when exposed) may have a measured coefficient of friction which of less than or equal to 0.5, and preferably 0.2 or less, when subjected to the test described hereinafter.

The bearing lining layer preferably comprises bronze. The overlay preferably layer comprises one or more of lead, tin, bismuth and copper.

Following is a description by way of example only and with reference to the figures of the drawings of modes for putting the present invention into effect.

In the drawings: Figure 1 is a cross sectional view of a plain bearing in accordance with the prior art.

Fqure 2 is a sectional view of an electrodeposited pure Ni coating in accordance with the phor art.

1 Figure 3 is a sectior',ai view of a pure Ni coating prepareu us:r1ç' ultrasound.

Figure 4 is a sectional view of a Ni composite layer with dispersed trihological particles in accordance with an embodiment of the invention.

Figure 5 displays particle size distribution data of diluted Watts bath solutions contaning 1 giL of hBN particles dispersed with method.s according to the poor art.

*) and the nventon.

Figure 6 displays particle size distribution data of diluted Watts bath solutions containing 1 gIL of MoS2 particles dispersed with methods according to the prior art and the invention.

Figure 7 displays particle size distribution data of diluted Watts bath solutions containing 1 gIL of WS2 particles dispersed with methods according to the prior art and the invention.

Figure 8 is an optical micro-section image of a Ni composite coating with hBN

particles in accordance with the prior art.

Figure 9 is an optical micro-section image of a Ni composite coating with hBN particles in accordance with example 4 of the invention.

Figure 10 is an optical micro-section image of a Ni composite coating with MoS2 particles in accordance with example 5 of the invention.

Figure 11 is an optical micro-section image of a Ni composite coating with WS2 particles in accordance with example 6 of the invention.

Figure 12 displays data obtained during tribological scratch tests performed on different electroplated Ni-based coatings.

Figure 13 is a schematic diagram of an electroplating process using ultrasound or megasound, according to an embodiment of the invention.

Figure 1 shows a schematic cross section of a plain bearing material 11 comprising a steel backing substrate 15 on which a Cu orAl based alloy lining material 14 is deposited. A Ni or Cu based alloy interlayer 13 is electrodeposited on the lining 14.

An overlay 12. is deposited over the interlayer F:ium 2 is a SEM crcss sect onci image of a ure Ni coating etectropiated from a Watts bath ac.tordmg to the or.or art. The Ni coating iayer 20 has been etectroplated withoul the use of ultrasound or megasound. The substrate 21 is a bearing material but could equally be another metal or rnetai alloy. A clear columnar structure 22 is present in the Ni coating.

Figure 3 is a SEM cross sectional image of a pure Ni coating prepared using ultrasound. The Ni. coating 30 has been etectropiated under ultrasonic irradation.

The substrate 31 Is a hearing material, hut couid equauy be another metal or metal alloy. The coating 30 has a more fragmented structure than the conventional coating shown in Figure 2. The coating 30 has higher proportion of refined grains 32 with fewer columnar crystals 33.

Figure 4 is a SEM cross sectional image of a Ni composite coating with particles dispersed evenly in a Ni metal matrix in accordance with an embodiment of the invention. The composite coating 40 has been electroplated under ultrasonic irradiation. The particles 41 are dispersed evenly in the Ni matrix 42. The substrate 43 is a bearing material, but could equally be another metal or metal alloy. The Ni matrix 42 is made of refined grains 44 with no columnar crystals.

Particle size distribution analysis Particle size distribution analysis was performed on Watts electrolytes containing different types of particles dispersed by different methods to show the improvement achieved in terms of particle dispersion in the electroplating bath when ultrasound or megasourid is used to disperse particles in the electroplating bath.

Example I

A diluted Watts electrolyte containing hBN particles, for use in a method according to the invention was prepared by: 1. Preparing a diluted Ni Watts bath with a pH of 3.2 and a temperature of 50°C.

2. Adding hBN particles (nominal size 1 pm) to the diluted Wafts bath. The resulting solution was treated with ultrasound and mechanical stirring for 30 minutes to achieve a fine dispersion of particles. The ultrasonic frequency was 35 kHz and the ultrasonic power was 0.2 W/orn3. The concentration of the particles was I gIL.

Example 2

A dfluted Watts eiectrclyte* containnq MoS2 parholes. tbr use in a method according to the invention was prepared by I. Preparing a diluted Ni Watts bath with a pH of 3.2 and a temperature of 50°C 2. Adding MoS2 particles (nominal size = 1 pm) to the diluted Watts bath. The resulting solution was treated with ultrasound and mechanical stirring for 30 minutes to achieve a ine dispe.rsion of particies. The uitrasonic frequency was:3S kHz and the uftrasonc power was 0.2 W/cm. The ooncentrat.on of the particles was gIL,

Example 3

A diluted Watts electrolyte containing WS2 particles, for use in a method according to the invention was prepared by: 1. Preparing a diluted Ni Watts bath with a pH of 3.2 and a temperature of 50°C.

2. Adding WS2 particles (nominal size = 0.6 pm) to the diluted Watts bath. The WS2 particles were in the powder form, and not the inorganic fullerene (IF) form. The resulting solution was treated with ultrasound and mechanical stirring for 30 minutes to achieve a fine dispersion of particles. The ultrasonic frequency was 35 kHz and the ultrasonic power was 0.2 W/cm3. The concentration of the particles was 1 gIL.

Comparative example I A diluted Watts electrolyte containing hBN particles, according to the prior art, was prepared by: 1. Preparing a diluted Ni Watts bath with a pH of 3.2 and a temperature of 50°C.

2. Adding hBN particles (nominal size = 1 pm) to the diluted Watts bath. The resulting solution was treated with mechanical stirring for 30 minutes. The concentration of the particles was 1 g/L.

Comparative example 2 A diluted Watts electrolyte containing MoS2 particles, according to the prior art, was prepared by: 1. Preparing a diluted Ni Watts bath with a pH of 3.2 and a temperature of 50°C, 2. Add!ng MoS: partcIes (nomina size' urn) to the diluted Watts bath. The esutnq soiution w s treated with mechanica strhno 1o 30 minutes ThE..' concerTh'atcn c/ the particles was I gil Comparative example 3 A diluted Watts electrolyte containing W52 particles, according to the prior art, was prepared by: Prepan'ng a diluted Nk Watts bath wah a phi of 3 2 arid a temperature ol 5000, 2. Adding WS2 particles (nominal size = 0.6 pm) to the diluted Watts bath. The WS2 particles were in the powder form, and not the inorganic fullerene (IF) form. The resulting solution was treated with mechanical stirring for 30 minutes. The concentration of the particles was 1 gIL.

Particle size distribution analysis of examples 1-3 and comparative examples 1-3 was performed by laser-diffraction.

Figure 5 is a graph depicting the size distribution of hBN particles dispersed in a diluted Watts bath electrolyte using two different methods: mechanical stirring (dashed line 51, comparative example 1) in accordance with the prior art, and a combination of ultrasound with mechanical stirring (continuous line 52, example 1) in accordance with an embodiment of the invention A better dispersion of hBN particles with smaller and more homogeneous size distribution is achieved with the invention.

Furthermore, the absence of very large agglomerates is achieved by using ultrasound.

Figure 6 is a graph depicting the size distribution of MoS2 particles dispersed in a diluted Watts bath electrolyte using two different methods: mechanical stirring (dashed line 61, comparative example 2) in accordance with the prior art, and a combination of ultrasound with mechanical stirring (continuous line 62, example 2) in accordance with an embodiment of the invention. A better dispersion of MoS2 particles with smaller size and more homogeneous size distribution is achieved by the invention Furthermore, the absence of very large agglomerates is achieved by using ultrasound Figure 7 is a graph depicting the size distribution of WS2 particles dispersed in a diluted Watts bath electrolyte using two different methods: mechanicai stirring 2 [dashed inc 71 comparative example 3 in accordance with the prior art, and a combination of citrascu nd with mecnanica stirring (continuous fine 72. example:3; in accordance with an embodiment of the invention, A better dispersion of WS2 particles with smaller size is achieved with (he presence of ultrasound.

fl all cases, a better dispersion of particles with a smaller size and more uniform spatial distribution was achieved when ultrasound was used. This shows the enhanced efficiency of using ultrasound or megasound in dispersing partic'es compared with other dispersing methods used in the prior art Analysis of particle dispersion in deposited tayers In 1.) The cross-sections of Ni-based composite coatings containing different types of tribological particles electrodeposited on Cu substrates, with and without ultrasound, were examined with an optical microscope. The results show the improvement in terms of particle incorporation and homogeneous spatial distribution achieved in Ni composite coatings when ultrasound is used during plating.

Example 4

A Ni composite coating containing hBN particles was prepared by: 1. Preparing a Wafts bath with a pH of 3.2 and a temperature of 50°C.

2. Adding hBN particles to the Wafts bath. The resulting solution was treated with ultrasound and mechanical stirring for 30 minutes to achieve an optimum dispersion of the particles. The ultrasonic frequency was 35 kHz and the ultrasonic power was 0.2 W/cm3. The concentration of the particles was 15 gIL.

3. The substrate to be plated was cleaned by vapour-degreasing in a hydrocarbon cleaner for 10 minutes.

4. The substrate was then mounted in a plating jig and anodic acid-etching pre-treatment of the bronze lining surface was applied at a current density of 3 A/dm2 for 2 minutes.

5. Electrodeposition of the NiIhBN composite coating on the Cu substrate was conducted at a current density of 4 A/dm2 for 20 minutes under mechanical stirring.

Ultrasound was also used during the plating process at a frequency of 35 kHz and an ultrasonic power of 0.2 W/cm3.

Example S

A N composite coating with MoS. partides was prpçp4 by: 1. Preparing a Watts bath wfth a pH of 3.2 and a temperature of 5Ot.

2. Adding Mo82 particles to the Watts bath. The resulting solution was treated with ultrasound and mechanical stirring for 30 minutes to achieve an optimum dispersion of particies The ultrasonic frequency was 35 kHz and the ultrasonic power was 0.2 VVcrn The concentration of the partcles was i 5 giL.

5. Electrodeposition of the Ni/MoS2 composite coating on the Cu substrate was conducted at a current density of 4 A/dm2 for 14 minutes under mechanical stirring.

JO Example 6

A Ni composite coating with WS2 particles was prepared by: 1. Preparing a Wafts bath with a pH of 3.2 and a temperature of 50°C.

2. Adding WS2 particles to the Watts bath. The WS2 particles were in the powder form, and not the inorganic fullerene (IF) form. The resulting solution was treated with ultrasound and mechanical stirring for 30 minutes to achieve an optimum dispersion of particles. The ultrasonic frequency was 35 kHz and the ultrasonic power was 0.2 WIcm3. The concentration of the particles was 15 gIL.

4. The substrate was then mounted in a plating jig and anodic acid-etching pre-treatment of the bronze lining surface was applied at a current density of 3 A/dm2 for 2 mnute 5, Electrodeposition of the N1IWS2 composto ccatng on to Cu substrate was conducted at a current densit,y of 4 Aidm2 for 4 minutes under mechanicat stirring.

Ultrasound was also used during the plating process at a frequency of 35 kHz and an ultrasonic power of 0.2 Wfcm3.

Comparative example 4 A Ni composite coating with hBN padicies according to the pnor ad was prepared by.

1. Preparing a vvatts bath with a oH of 3.2 and a temperature of SOt.

2. Adding hBN particles to the Watts bath. The concentration of the particles was 15 gIL.

5. Electrodeposition of the NiIhBN composite coating on the Cu substrate was conducted at a current density of 4 AIdm2 for 20 minutes under mechanical stirring, in the absence of ultrasound or megasound.

Comparative example 5 A Ni composite coating with Mo82 particles according to the prior art was prepared by: 1. Preparing a Watts bath with a pH of 3.2 and a temperature of 50°C.

2. Adding MoS2 particles to the Watts bath. The concentration of the particles was 15 gIL.

4. The substrate was then mounted in a plating jig and anodic acid-etching pre-treatment of the bronze lining surface was applied at a current density of 3 A/dm2 for 2 mnutes.

5. F ec.trodepcsiton of the NiMoS c.orr'poste coEtnç; on the Cu s.Thstrato was conducted at a cunent::1ensfv of 4 A/dm or 14 J&:; under unechanica1 shrrng.

the absence of ultrasound or megasound.

Comparative example 6 A Ni composite coating with W92 particles, according to the prior art was prepared by: 1. Preparing a Watts bath with a pH of 3.2 and a temperature of 50°C.

2. Adding WS2 particles to the Wafts bath. The WS2 particles were in the powder form, and not the inorganic fullerene (IF) form. The concentration of the particles was g/L.

5. Electrodeposition of the Ni/WS2 composite coating on the Cu substrate was conducted at a current density of 4 A/dm2 for 14 minutes under mechanical stirring, in the absence of ultrasound or megasound.

Figure 8 displays a cross sectional image of a Ni composite coating 80 (in accordance with comparative example 4) which has been electroplated in the absence of ultrasound. The hBN particles 81 are dispersed poorly in the Ni matrix 82 and are clumped together. The substrate 83 is a bearing material, but could equally be another metal or metal alloy.

Figure 9 displays a cross sectional image of a Ni composite coating 90 (in accordance with example 4) which has been electroplated under ultrasound. Unlike in comparative example 4 (figure 8), the fine hBN particles 91 are dispersed evenly in a Ni matrix 92 and are much less clumped together. The substrate 93 is a bearing material, but could equally be another metal or metal alloy.

Figure 10 displays a cross sectional image of a Ni composite coating 100 (in accordance with exampie 5) which has been electroplated under ultrasound. The fine MoS2 partides IC) I are dispersed evenly in the Ni matrix 102. The substrate 103 a 23 beanng niatenal, out conid equally be another metal or metal aioy. Whereas MoS? parflcles in example' 5 were successfully incorporated and eveny distributed within the Ni matrix, no acceptable coaling was produced for comparative example 5 Hence, no cross sectional images of comparative example 5 are included in the present application. In comparative example 5 a thick layer of a compacted sludgy deposit completely covered the surface of the substrate when plating was conducted in absence of ultrasound, Figure 11 displays a cross sectional view of a Ni composite coating 110 (in accordance with example 6) which has been electroplated under ultrasound. WS2 particles 111 dispersed evenly in the Ni matrix 112. The substrate 113 is a bearing material, but could equally be another metal or metal alloy. Whereas WS2 particles in example 6 were successfully incorporated and evenly distributed within the Ni matrix, no acceptable coating was produced for comparative example 6. In comparative example 6 the WS2 particles were electrophoretically deposited over the surface of the Cu substrate, thus inhibiting the electrodeposition of Ni. This layer of agglomerated WS2 would fall off the substrate quite easily after drying. There are therefore no cross sectional images of comparative example 6 in the present invention.

The results obtained for example 4 and comparative example 4 show the improvement in particle incorporation and distribution that is achieved when ultrasound is used during the electroplating process. The results observed for examples 5 and 6, when compared to comparative examples 5 and 6, demonstrate the importance of the use of ultrasound or megasound in preventing massive particle agglomeration and blocking of the substrate's surface.

Tribological performance analysis Pure Ni and Ni-based composite coatings containing different types of tribological particles were ultrasonically electrodeposited on Cu substrates in order to perform friction (scratch) tests. The tests show the improvement in tribological performance achieved in Ni coatings containing particles which have been deposited using processes according to the present invention. Cu is not the only substrate which may be employed. Other metals or metal alloys may also be used.

Dry scratch tests were peformed on afferent Ni*hased ccabnqs to observe the effect that the nccrporation ol soft partides has or The coeffice t of frctior of Ni coaflnq!, The condihons c the Feet were' * Sliding distance: 10mm1 * Sliding speed: 10 mm/mm, Load: 100 N (progressive), * BaU diameter. 6,3 mm, Ball material: JIS SUJ2 -ISO lOOCr6.

Example 7

A Ni composite coating with hBN particles was prepared by: I Preparing a Watts bath with a pH of 3.2 and a temperature of 50°C.

2. Adding hBN particles to the Watts bath. The resulting solution was treated with ultrasound and mechanical stirring for 30 minutes to achieve an optimum dispersion of fine particles. The ultrasonic frequency was 35 kHz and the ultrasonic power was 0.2 W/cm3. The concentration of the particles was 15 gIL.

3, The substrate to be plated was cleaned by vapour-degreasing in a hydrocarbon cleaner for 10 minutes.

5. Electrodeposition of the NiIhBN composite coating on the Cu substrate was IS conducted at a current density of 4 AIdm2 for 14 minutes under mechanical stirring, Ultrasound was also used during the plating process at a frequency of 35 kHz and an ultrasonic power of 0.2 W/cm3.

Example 8

A Ni composite coating with Mo82 particles was prepared by: 1. Preparing a Watts bath wTh a pH of 3.2 and a temperature of 50°C.

!.,Aridinq Mo52 pattdes to the Watts baTh. The resuftir?g soution was treated wth uRrasound and mechinca sUrrno Ci 30 mr?.utes to achieve an oumun diace sion of fine oartices. The uR.rasonc frequencywas 25 kHz and tne ultrasonic powe was 0.2 W/cm3. The concentration of the particles was 15 gIL.

Example 9

A Ni composite coating with WS2 particles was prepared by: 1. Preparing a Watts bath with a pH of 3.2 and a temperature of 50°C.

2. Adding WS2 particles to the Watts bath. The VVS2 particles were in the powder form, and not the inorganic fullerene (IF) form. The resulting solution was treated with ultrasound and mechanical stirring for 30 minutes to achieve an optimum dispersion of fine particles. The ultrasonic frequency was 35 kHz and the ultrasonic power was 0.2 W/cm3. The concentration of the particles was 15 gIL.

5. Electrodeposition of the NiIWS2 composite coaUng on the Cu substrate was conducted at a current densty of 4 A/dm 1cr 14 minutes under mecharcai stirring.

ijRrasound was aso usec. duriop the pating process at a frenuency ot 135 kH2., and an t.rasorc pniai of 0 2 W'c.m.

Example 10

A Ni composite coating with PTFE particles was prepared by: 1. Preparing a Watts bath containing 0.1 gIL of Capstone FS-3100 with a pH of 3.2 and a temperature of SOt.

2. Addition of PTFE particles to the Wafts bath. The resulting solution was treated with ultrasound and mechanical stirring for 30 minutes to achieve an optimum dispersion of fine particles. The ultrasonic frequency was 35 kHz and the ultrasonic power was 0.2 W/cm3, The concentration of the particles was 50 gIL.

4. The substrate was then mounted in a plating jig and anodic acid-etching pre-treatment of the bronze lining surface was applied at a current density of 3 AIdm2 for 2 minutes.

5. Electrodeposition of the Ni/ PTFE composite coating on the Cu substrate was conducted at a current density of 4 A/dm2 for 14 minutes under mechanical stirring.

Ultrasound was also used during the plating process at a frequency of 35 kHz and an ultrasonic power of 0.05 WIcm3.

Comparative Example 11 A Ni coating electrodeposited under ultrasound was prepared by: 1. Preparing a Ni Watts bath with a pH of 3.2 and a temperature of 50 °C 2. The substrate to be plated was cleaned by vapour-degreasing in a hydrocarbon cleaner for 10 minutes.

3. The substrate was then mounted in a plating jig and anodic acid-etching pre-treatment of the bronze lining surface was applied at a current density of 3 AIdm2 for 2 minutes.

4, F lctrdeposition of the pure M coating on the copper substrate was conducted.l.

a cuuent density of 4 Ndm2 for 14 minutes under mec anca stirring. Uirasound was used during the plating process at a frequency of 35 kHz. and an ullrasonic power of 0,2 WIcm3.

Comparative example 1 A Ni interlayer according to the prior art was prepared by L Preparing a Ni Watts bath wTh a pH of 3.2. and a temperature of 50 °C.

2. The substrate to be plated was cleaned by vapour-degreasing in a hydrocarbon cleaner for 10 minutes.

3. The substrate was then mounted in a plating jig and anodic acid-etching pre-treatment of the bronze lining surface was applied at a current density of 3 A/dm2 for 2 minutes.

4. Electrodeposition of the pure Ni coating on the copper substrate was conducted at a current density of 4 A/dm2 for 14 minutes under mechanical stirring.

Table 1 summarises the examples and comparative examples tested during the scratch tests.

Table 1

Ultrasound Material Bath Particle during Surfactant plating hBN 7 NiIhBN Wafts Yes No (lSg/L) MoS2 8 NiIM0S2 Watts Yes No (lSgIL)

Examples

\N82 I 9 Ni/WS2 Watts Yes No (1 5 gIL) H --t.-.---------FIFE r IQ NkPF JVats ret, (50 giL) I (0.ig/L) -----T ----.___.L__ 11 Ni Watts n/a Yes. No Comparative Examptes 7 Ni VVatts n/a n/a No ::... L. .-_..__.j.

Dry scratch tests for each of the examples and comparative examples were performed and are shown in Figure 12. The graph depicts the evolution of the coefficient of friction vs. testing time for examples 7-10 and comparative examples 7 and 11. The coefficient of friction measured for the different Ni materials is displayed in Table 2. The specimens prepared in accordance with embodiments of the invention showed in all cases a lower coefficient of friction than Ni coatings prepared by comparative examples 7 and 11.

Table 2

Material Coefficient of friction 7 Ni/hBN =0.48 8 Ni,WS2 =0.31 Invention

Examples I

9 Ni/MoS2 =0.41 Ni/PIFE t017 11 Ni r055 Comparative

Examples

7 Ni =0.66

I __________ --_________ _______

Fgure 13 is a schematk cross sectional represefltafon of a;' electropiating *apparatus fo carr$ ng out a proce a using trasonic and/or megasonc.agitatkni and fiud agtat;on to deposit cornoost.e coaflngs, in accordance. with the,nvenhon The electroplating tank 1301 is filled with an electrolyte solution 1302. The specimen to be coated 1303 is connected to the cathode of a rectifier 1304. A counter-electrode 1305 is connected to the rectifier 1304 and is set as an anode. An uitrasonic/megasonic transducer 1306 with its independent controller box 1307 is attached either inside or outside of the plating tank 1301 lo generate ultrasonic/megasonic waves 1311 shown schematically). These waves are used to disperse triboloç;cal paftotes 1308 in the plating electrolyte 1302, optionady when electrodepositirig a coating on the specimen 1303. A perforated pipe 1309 is connected to a circulatory fluid pump 1310. The fluid pump is used to generating fluid agitation in the electrolyte 1302.

Typical steps to work an embodiment of the current invention are: 1. Dispersing particles in the electrolyte using ultrasound or megasound prior to the electroplating process by operating the ultrasonic or megasonic transducers at a frequency of 10 to 3000 kHz and a power of up to 5W/cm3 for a period greater than 0.1 seconds. IJltrasonic/megasonic irradiation can be either continuous or pulsed.

The frequency and power ot the acoustic field improves the spatial dispersion and prevents the undesired formation of agglomerated particles.

2. Degreasing the substrate to be plated to remove any traces of grease or oil.

3. Mounting the substrate on a plating jig and pre-treating them to assure a good bonding of the interlayer to the substrate.

4. Immersing the substrate in the electrolyte used for the electrodeposition of the interlayer. Plating of the interlayer onto the substrate process is then carried out at a current density of up to 100 Ndm2. The current density and the plating time determine the thickness of the composite coating. Four different agitation conditions could be used in this step: i) ultrasonic/megasonic agitation, ii) combination of ultrasonic/megasonic and other agitation methods, iii) any agitation method or combination not involving ultrasound/megasound, and iv) no agitation.

5. Immersing the substrate with the deposited interlayer in another electrolyte to electrodeposit the overlay over the surface of the interlayer, in summary, the preseflt inventior relates to pain bearing cornpo&te mat.eria consisting o a backing substrate (e steei, a lining material (i a Cu-based or Ai based alloy), an interayer and an overlay (e.g. Pb*based, Snbased. PA-based o Cu-based alloys), where the nteriayer is an electrodeposited metal-based composite coating consisting of a metal matrix (i.e. Ni-based alloy) and uniformly and well-dispersed tribologically-useful particles.

Claims

CLAIMS1. A method of forming a plain bearing comprising: providing a backing substrate, with a bearing lining material deposited on the backing substrate, depositing an interlayer over the bearing lining material and depositing an overlay over the interlayer, wherein the interlayer is applied on the lining material by electroplating from a deposition bath in which tribologically useful particles are dispersed before and/or during electrodeposition of the interlayer by ultrasonic and/or megasonic agitation, and wherein the interlayer is thereby deposited as a composite of a metal matrix with a dispersion of said particles distributed therein.
2. A method according to claim 1 wherein the ultrasonic and/or megasonic agitation is applied to the particles before electrodeposition commences and optionally during electrodeposition.
3. A method according to claim 1 or claim 2 wherein the deposition bath is agitated by a further agitation method such as stirring, which may be conducted before and/or during electrodeposition.
4. A method according to any of the preceding claims, wherein the ultrasonic and/or megasonic frequency is between 10 and 3000 kHz, preferably from 15 to 200 kHz.
5. A method as claimed in any of the preceding claims wherein the ultrasonic and/or megasonic power is between 0.00001 and 50W/cm3, preferably from 0.0001 to 5 W/cm3,
6. A method according to any of the preceding claims, wherein the ultrasonic and/or me,gasor4c agitation and any other agEtation methods are apphed before 3.5 and/or dunng elect.nDaepositon for a period of time ionger than 3.01 seconds and no ionqe tar 60 days, creforat4y b&ween 20 seconds and 48 hours..
7. A method accordinq to ciam 6, wherein the uftrasorhc and/or megasonic agitation and any other agitation methods are applied before and/or during electrodeposition for a period of time between 1 minute and 24 hours, preferably between 5 minutes and 4 hours.
8. A method according to any of the preceding claims, wherein the ultrasonic and/or megasonic agitaton and any other agitation methods are applied as a series of puFses.
9. A method as claimed in claim 8, wherein the time on' during one pulse ranges between 0.0001 seconds to 24 days, and the time off during one pulse ranges between 0.0001 seconds to 24 days.
10. A method of manufacturing a plain bearing composite material according to claim 6, wherein the time on during one pulse could range between 0.001 seconds to 2 hours, and the time off during one pulse would range between 0.001 seconds to 2 hours.
11. A method according to any of the preceding claims, wherein the particles comprise soft particles with Mohs hardness «= 5.
12. A method as claimed in any of the preceding claims wherein the particles comprise hard particles with Mohs hardness> 5, preferably »=5.5.
13. A method as claimed in claims 11 and 12 wherein the particles comprise a combination of both soft (Mohs hardness «= 5) and hard (Mohs hardness> 5, preferably »=5.5) particles.
14. A method as claimed in any of the preceding claims wherein the particles deposited are of a uniform composition.
15. A method as claimed in any of claims ito 13 wherein the particles deposited comprise two or more sets of particles having different compositions.
16. A method as claimed in claim 11 or 13, wherein the soft particles are selected from the group of PTFE, fluorinated polymers, metal sulphides, metal fluorides, metal sulphates, graphite and other soft carbonaceous particles, hexagonal boron nitride, phyllosilicates, zinc oxide and lead oxide.
17. A method as claimed in claim 12 or 13, wherein the hard particles are selected from the group of metal oxides, borides, carbides. nitrides, sulphates and sThcides. diamond, carbon nanotubes, graphene and other hard carbonaceous parfices,.
18. A methc'd according to any of preceding caims. wherein at ieast 95% of the tribologica particles in the electrodeposition bath have diameters of 1 nm to 10 pm, preferably 250 rim to 2 pm, and most preferably 600 nm to 2 pm.
19. A method according to any of the preceding claims, wherein the interlayer metS matrix deposited by electroplating cornorises:9 metal selected from Ni, Cu, Cr..Co,Fe or aUoys based uron any of these metais
20. A method as claimed in any of the preceding claims wherein the tribological particles do not include inorganic fullerene-like WS2 particles.
21. A plain bearing comprising: a backing substrate, a bearing lining material deposited on the backing substrate, an interlayer deposited over the bearing lining material and an overlay deposited over the interlayer, wherein the interlayer is deposited as a composite of a metal matrix with a dispersion of tribologically useful said particles distributed therein.
22. A plain bearing according to claim 21 which is obtained by a method according to any of claims 1 to 20.
23. A plain bearing according to claim 22 wherein the interlayer when exposed has a coefficient of friction of less than or equal to 0.5, and preferably 0.2 or less, when subjected to the test on page 18 of the description.
24. A plain bearing according to any of claims 21 to 23 wherein the bearing lining layer comprises bronze.
25. A plain bearing according to any of claims 21 to 24 wherein the overlay layer comprises one or more of lead, tin, bismuth and copper.