friction and wear of electroless nip and nip+ptfe coatings

Wear 259 (2005) 828834

Friction and wear of electroless NiP anrandinhal deuarda, 6

ary 2002005

Abstract

In the pas tions tspace, and in el genewear resistan ies, solAn importan the abMoreover, i the EN(NiP + PTFE ity thaalloy deposi and wsliding conta coating 2005 Elsevier B.V. All rights reserved.

Keywords: Wear; Friction; Dissipated energy; Electroless coatings

1. Introdu

It is welthe autocatsolution intcurrent. ENthe physicasystems. Tchemical aand wear reregardlessnonmagnet

The meposits canparticles (Sbricants (Pcase in a filcharacteris

CorresponE-mail ad

0043-1648/$doi:10.1016/jction

l known that the electroless nickel (EN) coating isalytic deposition of a NiP alloy from an aqueouso a substrate without the application of an electriccoatings provide material properties that expand

l properties beyond those of pure nickel coatinghese coatings are widely used in the mechanical,nd electronic industries because of their corrosionsistance, hardness, lubricity, uniformity of depositof geometries, solderability and bondability andic properties [1].chanical and tribological properties of these de-be further improved by the incorporation of hardiC, B4C, Al2O3 and diamond) [2,3] and dry lu-

TFE, MoS2 and graphite) [1,35], resulting in thism with self-lubricating and excellent anti-stickingtics.

ding author. Tel.: +351 939306676; fax: +351 271220150.dress: [email protected] (J.C. Miranda).

The properties and microstructure of EN coatings dependon the post-deposition heat treatment, which is frequentlyused to improve adhesion or to modify properties in orderto satisfy the needs of a particular application. In this case,and with an appropriate temperature used in the heat treat-ment, there is an increase in the hardness reaching eventhat of commercial hard chromium coatings [2,6]. There-fore, for some applications, EN can be a good alternativeto the chromium coatings without the negative environmen-tal impact due to the chromium deposition [68]. As a re-sult of heat treatment, the characteristics of the deposit canbe changed, namely: wear, corrosion and fatigue resistance,hardness, ductility, magnetic properties and other. Maximumhardness can be achieved after a 1-h heat treatment above360 C, depending on the phosphorous content [1,2,9]. Thishas been attributed to fine Ni crystallites and hard intermetal-lic Ni3P particles precipitated during the crystallization of theamorphous phase [9,10]. Depending on the conditions of theheat treatment, the structure of the EN coatings has been re-ported to be either crystalline, amorphous or a mixture ofboth.

see front matter 2005 Elsevier B.V. All rights reserved..wear.2005.02.052A. Ramalho a, J.C. Mia Universidade de CoimbraFCTUC-Dep. Eng. Mecanica, Polo II, P

b Esc. Sup. de Tecnologia e Gestao, Inst. Politec. da G

Received 27 July 2004; received in revised form 24 JanuAvailable online 10 May

t 30 years, electroless nickel (EN) plating has grown to such propora myriad of areas in between. The first criteria to use electroless nickce, hardness, lubricity, uniformity of deposit regardless of geometrt property is the amorphous structure in the as-plated condition and

n order to improve the mechanical and tribological properties of) composite coating can be obtained that provides even greater lubrict. The aim of the present work was an investigation of the frictioncts against hard chromium steel. The role of heat treatment of thed NiP + PTFE coatingsa b,

Marrocos, P-3030-201 Coimbra, Portugal300-559 Guarda, Portugal

5; accepted 5 February 2005

hat these coatings are now found underground, in outerrally falls within the following categories: corrosion andderability and bondability and nonmagnetic properties.ility to heat treat the deposit by precipitation hardening.

coatings (NiP) further, a EN-polytetrafluoroethylenen that which naturally occurs in the nickelphosphorousear characteristics of NiP and NiP + PTFE coatings inis discussed.

A. Ramalho, J.C. Miranda / Wear 259 (2005) 828834 829

The present work aims to investigate the friction and wearcharacteristics of NiP and NiP + PTFE coatings in slidingcontacts against hard chromium steel. The role of heat treat-ment of the coating is discussed.

2. Experimental details

Friction and wear were experimentally studied using asliding tribometer with crossed cylinder contact (Fig. 1).The equipment included a rotating specimen with cylindri-cal shape (3) and a smaller cylindrical stationary specimen(5). The normal load was applied by a spindle/spring sys-tem (4) and was measured by a load cell (1). The stationaryspecimen, a hard steel AISI 52100 with 750HV30, with adiameter of 10 mm, was supported by a free rotating sys-tem, which was equilibrated by a second load cell (2) used tomeasure the friction force. The diameter of the rotating discwas 60 mm and the rotation speed 159 rpm, thus, the slidingspeed was 0.5 m/s. This disk, of a hard high-speed steel AISIM2 quenched and tempered with 880HV30, was used as asubstrate to deposit the EN coatings. The normal load wasin the range from 2 to 35 N and the test duration from 4 minto 30 h, which correspond to a sliding distance from 120 to54,000 m.

The coatings were produced in an industrial plant by Tec-nocrom Indelectroless

Five maNiP as-plaplated, NiPcoated AIS

Fig.

Before testing, the specimens were cleaned with ethylicalcohol. During the test, the friction force value was periodi-cally acquired, with time intervals oft. In each acquisition, aset of several thousand values was collected, corresponding toan acquisition time larger than the rotation period. Therefore,the average values of the friction force, Fa calculated fromeach set of acquired data, correspond to the average value ofthe friction. The friction that exists in the crossed cylindercontact is responsible for an energy dissipation [11,12]. Thisfact leads to the occurrence of wear in the materials. Consid-ering that the friction is the most important process relatedto the changes in the system energy, it would inevitably playan important role in the wear losses. In this way, the energydissipated in the contact can be calculated as the work ofthe friction force. For each time interval t, to which cor-responds a displacement x, the dissipated energy E canbe achieved by Eq. (1). Considering the average value of thefriction for(2) can be u

E =

0

E = Fa VThe total eby adding a

test tscar (

n thetial trear sc

usino [13]ler tha

2h2

e d1 iseter o

ch scr, a, a

Figustrial S.A. (Barcelona, Spain) using commercialnickel solutions.terials were tested against AISI 52100, namely,ted, NiP heat treated (HT NiP), NiP + PTFE as-+ PTFE heat treated (HT NiP + PTFE), and un-

I M2 steel.

1. Sliding tribometer with crossed cylinder contact.

of thewear

Oferenthe wshapemalhsmal

V =

wherdiamscar.

Ealargece and assuming a constant sliding speed Vt, Eq.sed.l

Fa dx = t

0Fa Vt dt (1)

t t (2)nergy dissipated during the test can be calculatedll theE calculated throughout the test. At the endhe stationary specimen shows an elliptical-shapedFig. 2).rotating specimen, the wear produces a circum-ack. For the stationary specimen, the volume ofar can be calculated assuming an imposed wear

g the approximate expression (3) derived by Ra-. This simple equation is very accurate with errorsn 0.2% [13].

d1d2 (3)

the diameter of the stationary specimen, d2 is thef the rotating specimen, and h is the depth of the

ar is measured by taking the dimensions of thend the smaller, b, dimensions of the wear surface

. 2. Typical wear scar of the stationary specimen.

830 A. Ramalho, J.C. Miranda / Wear 259 (2005) 828834

Fig. 3. The scanning electron micrographs of as-deposited coating

(Fig. 2). Thpublication

The chethe coatinganalyses (Eelectron miformed in a

Some ofwere heat tness was m

Vickers ind

3. Results

All the c8m, whic[14].

SEM waobserve thesurface ofposite coatnickelphoof the coatithe value o

XRD won the coat

1gs mic

ial

PTFE

posite(Fig

ngs cridentie effe

g theent.

ng thang harphase 3ting from the heat treatment. Similar results were ob-d by Shoufu et al. [10].general, the wear of the moving specimens could not

easured because of two reasons: the EN coatings werehard with a very small wear track; in the cases whereack was more in depth, the value of the roughness ofubstrate made it impossible to accurately evaluate thesponding wear volume. Only the wear of the stationaryis calculation method is well explained in an early[12].

mical composition, structure and morphology ofs were characterized with electron probe micro-PMA), X-ray diffraction (XRD) and scanning

croscopy (SEM), respectively. The XRD was per-Philips X-Pert with a Co K radiation.the EN specimens used for friction and wear tests

reated at 290 C for 10 h. The coatings microhard-easured using a Struers Duramin equipment withenter and a load of 50 g applied for 15 s.

and discussion

oatings studied had a thickness of approximatelyh was measured by the crater grinding method

s used to examine the coating surfaces in order tomorphology details (Fig. 3). In this picture, the

the NiP coating appears very dense and the com-ings display large PTFE particles embedded in thesphorous matrix. The average surface roughnessngs was similar for both NiP and NiP + PTFE withf 1.12m (Ra).as used to analyse the effect of the heat treatment

TableCoatin

Mater

NiPNiP +

as-dePTFEcoatiwere

Thsurintreatmvealicoatihardresultaine

Inbe mverythe trthe scorreing structure. The X-ray spectra reveal that in the specimen h

Fig. 4. X-ray diffraction pattern of EN coatings: (a) NiPs: (a) NiP and (b) NiP + PTFE.

rohardness

Hardness (MPa)As-plated Heat treated

5660 95604880 7250

d state, films are amorphous either with or without. 4). In both cases, the heat treatment leads to theystallization and the phases -Ni, NiP and Ni3Pfied.ct of the crystallization was first analysed by mea-surface microhardness before and after the heatTable 1 represents the average microhardness, re-t the heat treatment significantly improves thedness. The formation and fine dispersion of thes NiP and Ni P justify the rise in microhardnessas been evaluated applying Eq. (3). For each test

and (b) NiP + PTFE.


Table 2Wear results of all the performed tests

Materials Case Normal load (N) Sliding distance (m) Wear volume (mm3) Dissipated energy (J)NiPAISI 52100 1 2 300 0.0037 269.05

2 2 450 0.0070 606.003 5 450 0.0307 1108.124 5 120 0.0386 1841.165 5 600 0.0395 406.00

HT NiPAISI 52100 6 5 3600 0.0019 9005.997 2 10800 0.0008 11064.968 5 8100 0.0030 19397.339 2 27000 0.0058 29438.14

10 3 54000 0.0216 95970.11

NiP + PTFEAISI 52100 11 2 9000 0.00057 9648.6612 2 14400 0.0008 16585.1713 5 12150 0.0018 47196.87

HT NiP + PTFEAISI 52100 14 5 9000 0.00071 27193.5215 5 18000 0.0043 61256.3716 10 9000 0.0034 62266.79

AISI M2AISI 52100 17 5 900 0.0777 2510.6918 5 1800 0.2815 6925.81

the dissipathe proceduperformed

The prodescribed,presented ivolume remthe NiP coof the tests

Besidesalso calculawas generadividing thnormal loa

k = VXL

classiear vo

al loaveralng to Elope olidingned rewear r

imume expeble 3ge vats obta

Fig. 5. W19 2 900

ted energy has been calculated using Eq. (2) andre was outlined. Table 2 shows the results of all

tests.cedure based on the dissipated energy, previouslywas applied to all the tested cases. The resultsn Fig. 5 have good linear correlation between theoved by wear and the dissipated energy. However,

ating shows a lower correlation, because in somethe substrate was locally reached.the energetic approach, a specific wear rate wasted. The wear coefficient or specific wear rate, k,

lly calculated based on the Archard [15] equation,e wear volume by the sliding distance and thed:

Thisthe wnorm

for secordithe sXL (sobtaicifica minof th

Taavera

resul(4)ferent mate

Fig. 7(aedge of the

ear volume against dissipated energy on the tested materials. (NiP + PTFE data in0.0189 480.27

cal approach is based on the linear evolution oflume, V, with both the sliding distance X and the

d L. In the present work, the wear tests were donenormal loads and sliding distances. Therefore, ac-q. (4) the specific wear rate k can be calculated as

f the linear evolution of the wear volume againstdistance times normal load). Fig. 6 displays the

sults. The slope of the linear equations is the spe-ate values. The tested materials fit linear laws withcorrelation of 0.93 expressing adequate accuracy

rimental results.summarises the wear results, also including the

lue of the friction coefficient. If we compare theined by both approaches, the ranking of the dif-

rials is similar.) shows that the NiP coating lifted up close to thewear track. This reveals that these films have poor

tegrates the NiP + PTFE and the HT NiP + PTFE points.)


Fig. 6. Wear volume against XN for the tested materials. (NiP + PTFE integrates the NiP + PTFE and the HT NiP + PTFE points.)

Table 3Average values of the friction coefficient and wear rates

Materials Specific wear rate (mm3/N m) Energy wear rate (mm3/J) Friction coefficientNiP 1.52 105 1.52 105 0.62HT NiP 2.37NiP + PTFE 6.45HT NiP + PTF 6.45AISI M2 3.11

adhesion. Wlift up and(Fig. 7(b)).hardness, leimproving

The resulowing:

AdherennificantlAISI M2proxima

Heat trehaviour

ncerns notce.

omparthe cs of mevious1.44 1074.76 108

E 4.76 1083.74 105

hen tested after heat treatment, the film did notwe can see a mild evolution of the wear trackThus, the heat treatment, beyond the increase inads to higher adhesion of the film to the substrate,

markedly the wear behaviour.lts of the wear study can be summarized as fol-

t NiP coatings, with or without PTFE, have sig-

Cowa

tan

Cings,orderto pry superior properties to the hard high-speed steel, leading to lower specific wear rates k, up to ap-

tely 3 orders of magnitude.atment noticeably improves the tribological be-of the NiP coatings.

not to be etion to thetheir lowereffect of thdissipation(Fig. 7(a)),

Fig. 7. The scanning electron micrographs of wear tracks: (a) NiP107 0.53108 0.83108 0.7105 0.53

ing the NiP + PTFE coatings, the heat treatmenteffective on the improvement of the wear resis-

ing the results obtained for the as-deposited coat-oating with PTFE displays a wear coefficient 2agnitude lower than the NiP. However, contraryly expected view, the addition of PTFE seems

ffective on the friction reduction. The explana-highest behaviour of NiP + PTFE, in spite ofhardness (Table 1) could be dependent on the

e mild PTFE particles (Fig. 3(b)) on the stress. The NiP coatings display a significant spallingprobably due to their high level of internal stress,

as-deposited and (b) HT NiP.


iP and

while themoved.

The testnot effectivby the factfriction andance the effthe PTFE pthat the NiNiP + PTFEthe PTFE ppits clearlycoefficientto measureit was too s

In Figs.the NiP + Psented by ththat the expTherefore,does not inbe related tin the HT Ncoating.

4. Conclu

In this selectrolessticles was isubstrate wcoatings wsteel AISI 5geometry w

ll theigh-spn thehe films-dephe heoncerery efoatings-dephe intoating

owled

is woFig. 8. Worn surface morphology: (a) HT N

NiP + PTFE coatings were always gradually re-

results show that the addition of PTFE seems to bee in the friction reduction. This can be explainedthat the phosphorus content by itself leads to lowthe PTFE lubrication effect is not enough to bal-

ect of increasing the surface roughness induced byarticles. A detailed view of the wear tracks revealsP coating is worn by a fine abrasion, whereas the

shows local fractures in the neighbourhoods ofarticles identified by the arrows in Fig. 8(b). Theseincreased the roughness values, and so the frictionwas also increased. However, it was not possiblethe roughness directly on the wear track becausehort, approximately between 100 and 200m.5 and 6 the experimental points corresponding toTFE with and without heat treatment are repre-

(1) Ah

(2) Ita

(3) TCv

c

a

(4) Tc

Ackn

Th

e same line because the results obtained revealederimental points fit the same linear relationship.in spite of the hardness rise, the heat treatmentcrease the wear resistance. Certainly, this couldo the same local fractures, which could be deeperiP + PTFE, because of the lowest plasticity of the

sions

tudy, the friction and wear behaviour of severalNiP and NiP composite coatings with PTFE par-nvestigated. The hard high-speed steel used as aas also tested, as a reference. Some of the EN

ere heat treated. Dry sliding tests against a hard2100 counterface with a crossed cylinder contactere carried out. The results showed that:

the Portug(POCTI/33help of Teccoatings.

Reference

[1] Lai-GuielectroleFilms 24

[2] I. Apachless Nimicrohar134713

[3] Y.S. Huelectrole167 (200

[4] G. Strafftroless N(b) NiP + PTFE.

coatings improve the wear behaviour of the hardeed steel AISI M2 substrate.EN deposits, and due to the weak adherence of, the worst results were obtained for the NiP film

osited.at treatment produces films with higher hardness.ning the wear resistance, the heat treatment wasfective on the NiP coatings, while the NiP + PTFE

reveals the same wear resistance in both cases:osited and heat treated.roduction of PTFE particles in the electroless NiPs produces a significant rise in the wear resistance.

gements

rk was carried out under a project funded by

uese Foundation for Science and Technology710/EME/2000). The authors acknowledge thenocrom, S.A., Barcelona, Spain, in providing EN

s

Yu, Xu/Shou Zhang, The friction and wear properties ofss Ni-polytetrafluoroethylene composite coating, Thin Solid5 (1994) 98103.itei, J. Duszczyk, L. Katgerman, P.J.B. Overkamp, Electro-P composite coatings: the effect of heat treatment on thedness of substrate and coating, Scr. Mater. 38 (9) (1998)53.ang, X.T. Zeng, I. Annergren, F.M. Liu, Development ofss NiPPTFESiC composite coating, Surf. Coat. Technol.3) 207211.elini, D. Colombo, A. Molinari, Surface durability of elec-iP composite deposits, Wear 236 (1999) 179188.


[5] Q. Zhao, Y. Liu, H. Muller-Steinhagen, G. Liu, Graded NI-P-PTFEcoatings and their potential applications, Surf. Coat. Technol. 155(2002) 279284.

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[7] D. Barker, Electroless deposition of metals, Trans. Inst. Metal Finish71 (1993) 121.

[8] L.M. Wing, Use of electroless nickel on automotive components,Trans. Inst. Metal Finish 75 (1997) B11.

[9] R. Taheri, I.N.A. Oguocha, S. Yannacopoulos, The tribologicalcharacteristics of electroless NiP coatings, Wear 249 (2001) 389396.

[10] L. Shoufu, M. Erming, L. Pengxing, The effect of crystallizationon the wear resistance of electroless deposited NiP amorphous

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[11] M.Z. Huq, J.-P. Celis, Expressing wear rate in sliding contacts basedon dissipated energy, Wear 252 (2002) 375383.

[12] A. Ramalho, J.C. Miranda, The relationship between wear and dis-sipated energy in sliding systems, Wear (in press).

[13] A. Ramalho, Micro-scale abrasive wear test of thin coated cylindricalsubstrates, Tribol. Lett. 16 (1) (2004) 133141.

[14] European Standard EN1071-2, Advanced technicalceramicsmethods of test for ceramic coatings: Part 2. De-termination of coating thickness by the crater grinding method,2002.

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Friction and wear of electroless NiP and NiP+PTFE coatingsIntroductionExperimental detailsResults and discussionConclusionsAcknowledgementsReferences

friction and wear of electroless nip and nip+ptfe coatings

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