8/18/2019 Lub Wear

1/11

Wear 250 (2001) 631–641

Fretting wear behavior of TiB2-based materials againstbearing steel under water and oil lubrication

B. Basu, J. Vleugels, O. Van Der Biest∗

 Department of Metallurgy and Materials Engineering, Katholieke Universiteit Leuven, W. De Croylaan 2, B-3001 Leuven (Heverlee), Belgium

Abstract

Lubricated fretting tests in water and paraffin oil were performed with a monolithic TiB 2, a TiB2-based cermet with 16 vol.% Ni3(Al, Ti)

binder, a sialon–TiB2  (60/40) composite and a ZrO2–TiB2  (70/30) composite against ball bearing grade steel. Based on the measured

friction and wear data, the ranking of the investigated fretting couples was evaluated. Furthermore, the morphological investigations of the worn surfaces and transfer layers are carried out and the wear mechanisms for the investigated friction couples are elucidated. While

fretting in water, experiments revealed that tribochemical reactions, coupled with mild abrasion, played a major role in the wear behavior

of the studied material combinations. ZrO2–TiB2  (70/30)/steel wear couple has been found to have the highest fretting wear resistance

among the different tribocouples under water lubrication. Under oil lubrication, extensive cracking of the paraffin oil at the fretting contacts,

caused by tribodegradation, leads to the deposition of a carbon-rich lubricating layer, which significantly reduced friction and wear of all

the investigated tribosystems. © 2001 Elsevier Science B.V. All rights reserved.

Keywords: TiB2; Lubrication; Fretting wear; Tribochemical wear

1. Introduction

Ceramics are a promising class of advanced materials,which have a tremendous potential for tribological applica-

tions. During the last few decades, much attention has been

paid to investigate the wear and friction characteristics of 

several engineering ceramics [1]. Due to its high hardness

(around 25 GPa), TiB2   is considered to be a promising

material for tribological applications [2]. The poor sinter-

ability and rather low toughness however restricts the use

of the monolithic TiB2   in engineering applications. Differ-

ent binders are used to fabricate the TiB2-based technical

ceramics. In the present work, the wear behavior of a

monolithic TiB2, a sialon-based 40 vol.% TiB2  composite,

a ZrO2-based 30 vol.% TiB2  composite, and a TiB2-basedcermet with 16 vol.% Ni3(Al, Ti) binder is investigated. The

proposed applications of the investigated materials include

ball valves as pump components and grinding quills for

high-speed grinding operations, etc. In these applications,

fretting wear seems to cause a considerable loss in the

functionality of these materials. The unlubricated wear per-

formance of several advanced ceramics (e.g. zirconia, SiC,

silicon nitrides, etc.) demonstrated the need for lubrication

∗ Corresponding author. Tel.:  +32-16-32-1264; fax:  +32-16-32-1992.

 E-mail address:  omer.vanderbiest@mtm.kuleuven.ac.be

(O. Van Der Biest).

at the tribocontacts for the successful application as struc-

tural parts [3]. In this perspective, the present paper reports

the influence of different lubrication (distilled water andparaffin oil) on the tribological behavior of the TiB2-based

ceramics and cermets when fretted against ball bearing

steel. Because of its tremendous engineering importance,

steel is selected as the counterbody material.

The influence of different lubricants (water, paraffin oil)

on the wear behavior of a range of ceramics including alu-

mina, SiC, yttria-doped zirconia and Si3N4  have been com-

pared with that under dry sliding conditions [4]. Based on

the results, wear maps of these materials in different envi-

ronments have been established and the transitions in wear

behavior as a function of testing parameters (load and sliding

speed) are discussed. The same group of researchers studied

the mechanism of sliding wear of self-mated yttria-stabilized

tetragonal zirconia ceramics (Y-TZP) ceramic in different

lubricating media [5]. Oscar Barceinas-Sanchez and Rain-

forth recently investigated the sliding wear of a 3Y-TZP

ceramic against Mg-PSZ in distilled water and dry condi-

tions [6]. Water was found to provide modest lubrication,

lowering the sliding wear rate by a factor of three. The role

of humidity on the fretting wear of self-mated Y-TZP was

recently investigated in our laboratory [7].

Liu and Xue [8] constructed a “wear map” for a zirco-

nia/steel couple sliding in water. In another study, Kalin et al.

[9] carried out an extensive investigation to understand the

0043-1648/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved.

PII: S 0 0 4 3 - 1 6 4 8 (0 1 )0 0 6 7 0 - 6

8/18/2019 Lub Wear

2/11

632   B. Basu et al./ Wear 250 (2001) 631–641

fretting wear mechanisms of silicon nitride ceramics against

construction grade steel under water and formulated oil en-

vironments. It was observed that the presence of an an-

tiwear phosphorus additive in the formulated oil provided

more chemical protection to the worn surfaces compared to

the purified paraffin oil. Lubricated wear tests in engine oil

revealed a reduction in the wear rate of a Si3N4–TiC/steelfriction couple by four orders of magnitude as compared to

that in dry sliding conditions [10].

It should be noted here that the majority of the published

work cited above is based on pin-on-disk or ball-on-plate

tribometers under unidirectional sliding mode. Very few lit-

erature reports, for example [9], focus on the fretting wear

(linear reciprocatory displacement sliding) behavior of ce-

ramics in a lubricating medium. It can be pointed out here

that the wear of a given material combination depends on

many influential factors like the contact configuration, the

mechanical properties (hardness, toughness), testing param-

eters (normal load, sliding speed), microstructure (grain size,

porosity, etc.), the interaction with surrounding atmosphere

(relative humidity, water or other lubricants), etc. According

to the best of the authors’ knowledge, no fretting tests on

TiB2-based ceramics against steel in lubricating media are

reported in the literature.

In the present study, the lubricated wear behavior of 

TiB2-containing materials fabricated with different binders

(Y-TZP, sialon, and intermetallic) is investigated. The inves-

tigated materials including the TiB2  monolith have a range

of properties: hardness ranging from 13 to 21 GPa, frac-

ture toughness from 5 to 10 MPa m1/2, and elastic modulus

from 258 to 500GPa. The influence of physico-chemical

and mechanical properties of the different materials on thewear behavior, when fretted against steel under water and

oil lubrication will be elucidated. This will also assess the

suitability of the investigated binders in terms of providing

the optimum fretting wear resistance of TiB2  materials.

2. Materials and experimental procedure

2.1. Materials

The mechanical properties of the materials used in the

present work are listed in Table 1. Commercial bearing grade

Table 1

Mechanical properties of the ceramics used in the present investigation a

Flat material HV10   (GPa)   K Ic   (10kg) (MPa m1/2)   E  (GPa)

Monolithic TiB2   21.3  ±  0.7 5.6  ±  0.4 500

TiB2-based cermet (84/16) 16.1  ±  0.4 9.5  ±  0.7 476

Sialon–TiB2   (60/40) 16.6  ±  0.3 6.2  ±  0.4 365

ZrO2–TiB2   (70/30) 13.0  ±  0.2 9.7  ±  0.6 258

Steel counterbody (10 mm diameter ball)

DIN 100Cr6 grade 7.8  ±  0.1 20  ±  1.0 210

a The counterbody data are supplied by the commercial supplier.

steel balls (DIN 100Cr6 grade, Fritsch, Germany), 10 mm

diameter with mirror finished surfaces (surface roughness of 

0.02m, data from the supplier) were used as counterbody

materials. As provided by the supplier, the nominal compo-

sition (wt.%) of the steel ball includes C (2.1), Cr (12.0), Si

(0.3), Mn (0.3), and rest Fe.

The TiB2   monolith was processed from the finest ESKgrade TiB2 with 5 vol.% SiC (grade 059S, Superior Graphite

Co.) as sinter additive. According to the supplier, the Fis-

cher particle size of the ESK grade TiB2 powder is 

8/18/2019 Lub Wear

3/11

 B. Basu et al. / Wear 250 (2001) 631–641   633

Fig. 1. Representative microstructures of the investigated materials: (a) monolithic TiB2; (b) TiB2–Ni3(Al, Ti) (84/16); (c) sialon–TiB2   (60/40); (d)

ZrO2–TiB2  (70/30). Detailed description of the phase assemblage is presented in Section 2.

the TiB2-based cermet material, coarse boride particles

(4–5m, grey color) are dispersed in an intermetallic

Ni3(Al, Ti) binder, bright contrast (see Fig. 1b). The black 

particles in the cermet microstructure are Al2O3  phase. The

matrix phase of the sialon-based TiB2 composite (dark con-

trast in Fig. 1c) consists of both -Si3

N4

 and -sialon with a

low substitution ( z) value. The intergranular phase contains

yttria. The boride particles are in bright contrast. The differ-

ent phases that can be distinguished in the zirconia-based

composite (see Fig. 1d) on the back-scattered electron

micrographs are: ZrO2   (white), TiB2   (grey), and Al2O3(black). The presence of alumina is due to the use of alu-

mina milling balls during powder mixing. XRD investiga-

tions revealed the presence of a small amount of monoclinic

ZrO2  in the Y-TZP-based composite materials. A detailed

microstructural characterization and more information on

the mechanical properties of the zirconia composite are re-

ported elsewhere [13]. As observed in the microstructures

of the different composites, the homogeneously dispersed

TiB2  particles are irregularly shaped.

2.2. Fretting tests

The fretting experiments have been performed on a

computer-controlled tribometer under ambient temperature

(25◦C) and humidity (50–55% RH) conditions. The de-

tails of the experimental set-up can be found elsewhere

[14]. The ball-on-plate configuration is used and fretting

vibration at the contact is actuated by a linear relative dis-

placement of constant stroke (mode I, linear reciprocatory

relative displacement sliding). The flat samples are ground

and polished until they have an average surface roughness

( Ra) of 0.05m. The nominal dimensions of the flat sample

include a length of 20 mm, a width of 5 mm, and a height

of 3 mm. Prior to the fretting experiment, the materials are

ultrasonically cleaned in acetone. Two lubricants are used

8/18/2019 Lub Wear

4/11

634   B. Basu et al./ Wear 250 (2001) 631–641

in the present work: laboratory distilled water and commer-

cial paraffin oil (

8/18/2019 Lub Wear

5/11

 B. Basu et al. / Wear 250 (2001) 631–641   635

Fig. 3. The wear volumes of the TiB2-based flat materials and construction grade steel counterbody when fretted in water (a) and the wear volume of 

steel balls under oil lubrication (b). The fretting conditions are the same as mentioned in Fig. 2.

The wear volume of the TiB2-based flat materials fretted

against 100Cr6 ball bearing grade steel under water lubrica-

tion is shown in Fig. 3a. The error bars represent the standard

deviation of the wear data obtained from at least three fret-

ting tests. Both the monolithic TiB2  and TiB2-based cermet

show comparable volumetric wear. The wear volume of the

sialon-based composite is a factor of two higher than all the

other investigated material combinations, whereas the wear

volume of the zirconia composite is the lowest. The steel

balls experienced a high wear loss during fretting in water, as

revealed in the data presented in Fig. 3a. It should be noted

here that the counterbody wear is found to be one order of magnitude higher than that of the flat. The volumetric wear

of the steel counterbody follows the same trend as the wear

of the flat material. The highest ball wear is observed after

testing against the sialon composite, while the lowest with

the zirconia composite. Considering the total wear of the

tribocouples, it is clear that the sialon–TiB2 /100Cr6 grade

steel couple is most prone to fretting wear, whereas the zir-

conia composite/steel combination exhibits the highest fret-

ting wear resistance under water lubrication conditions. It

should be mentioned here that the wear data, measured on

the flats, do not show any clear relationship with the me-

chanical properties (see Table 1 and Fig. 3a). This indicates

that tribomechanical wear does not play any dominant role

in the present case.

3.1.2. Morphological investigation of the worn surfaces

The worn surfaces in the ‘monolithic TiB2 /steel

tribocouple’ after fretting in water are illustrated in Fig. 4.

A tribolayer is found to adhere to the mild abrasive grooves

on the TiB2   material, as shown in Fig. 4a. The presence

of numerous cracks on the tribolayer shows its brittle,

non-protective nature. EDS spectra acquired from such

layer indicates the formation of iron oxides, Ti oxides or

mixed (Fe, Ti) oxides (see Fig. 4b). Silicon from the silicon

carbide sinter aid was not detected on the worn surfaces.

Considering the water lubricating conditions, the presence

of hydroxides of Ti and/or Fe is also possible. The differ-

ent oxidized species, as will be reported throughout this

paper, can also exist in the hydroxide form under water

lubricating condition. A tribolayer, adhered to the relatively

deep abrasive groves, is observed on the steel counterbody

(Fig. 4c). Closer look at Fig. 4c also shows the adherence

of the tribochemical layer onto the worn steel surface. El-

emental analysis indicated the presence of Fe, Ti, Cr, O in

the tribolayer (see Fig. 4d). The presence of Ti on the worn

steel surface can be explained in either of two ways. Thefirst one is that TiB2  phase from the flat is oxidized during

the fretting process and incorporated in a transfer layer

(third body) between the mating couple. Another possibility

is that TiB2  particles are spalled off from the flat and then

transferred to the steel ball and finally oxidized. Both of 

these factors seem to be plausible. It can be mentioned here

that recent XPS investigation in our laboratory revealed that

the material transferred between the mating counterbodies

are always oxidized in the monolithic TiB2 /steel tribocouple

under unlubricated fretting conditions [17]. Following this,

it is more probable that TiB2  is oxidized and incorporated

in the iron oxide-rich tribolayer. Therefore, experimental

observations indicate the occurrence of tribochemical re-

actions with the mutual transfer of material between the

fretting couple and spalling of the tribochemical layer as the

major wear mechanism of the monolithic TiB2 /steel fretting

couple.

The worn surface in the ‘TiB2-based cermet/steel

tribosystem’ after fretting in water is presented in Fig. 5.

The fretted surface is characterized by the presence of 

strongly embedded thick wear debris particles, as shown

in Fig. 5a. Mild abrasive scars are noted in the flat worn

surface around the debris particles. EDS spectra obtained

from the debris show a strong Ni peak along with peaks of 

8/18/2019 Lub Wear

6/11

636   B. Basu et al./ Wear 250 (2001) 631–641

Fig. 4. Worn surfaces and EDS spectra of the tribolayers on the TiB 2  monolith ((a) and (b)) and steel ball ((c) and (d)) after fretting in water. Numerous

cracks could be readily observed in the tribolayer on the flat worn surface. EDS spectra ((b) and (d)) are acquired from the spots indicated by the arrows

in (a) and (c). The arrow in (c) also indicates typical adherence of the tribochemical layer. The tribolayer next to it is predominantly iron oxide. The

fretting direction is indicated by a doubly pointed arrow.

Fe, Ti, Cr, Al, and O (see Fig. 5b). The worn steel ball is

observed to be covered by a tribolayer, as shown in Fig. 5c.

The EDS spectrum of the tribolayer on the steel indicates

the presence of Fe, Ni, Cr, and O (see Fig. 5d). Although,

Ti is not recorded in the reported spectrum, Ti is found

in other investigated locations on the worn steel ball. The

fact that Fe is present on the flat indicates that iron oxide

is transferred from the steel ball onto the flat. The pres-

ence of Ni on the worn steel surface indicates that NiO is

dissolved in the iron oxide layer on the worn steel. The for-

mation of NiO indicates the tribochemical oxidation of the

intermetallic binder phase in the cermet during the fretting

process.

As-fretted surfaces in the ‘sialon–TiB2 /steel combination’

after fretting in water is shown in Fig. 6. A thin tribofilm is

found to cover the flat worn surface (see Fig. 6a). Closer look 

at the flat worn surface reveals the presence of numerous mi-

crocracks in the tribolayer. This indicates the non-protective

nature of the tribofilm. The compositional analysis of the

tribofilm revealed the presence of Si, Ti, Fe, Cr, and O,

as shown in Fig. 6b. The amount of iron oxide transferred

from the steel ball is significantly smaller than that in the

previous cases, as evident from the fairly weak Fe peak. The

strong Si peak in combination with the strong O peak sug-

gests the formation of silica. Deep abrasive scars could be

seen despite the presence of a tribochemical layer on the

worn steel ball (see Fig. 6c). The EDS spectrum of the tri-

bofilm reveals the presence of high amounts of Si and Ti (see

Fig. 6d). No significant amounts of Fe and Cr were measured

in the tribolayer. This indicates the transfer of the mixed and

probably hydrated Si–Ti oxide layer on the worn surface

of the steel ball. The compositional analysis, as described

above thus shows the possible material transfer and tribo-

chemical oxidation of the sialon binder phase and TiB2 onto

steel counterbody. It is reported in the literature [4,9,18] that

silica can get dissolved into water forming silicon hydroxide

or hydrated silica under the water lubricating conditions at

the tribocontact. When silicon nitrides slide in water, the tri-

bochemical reaction is reported to be the dissolution of silica

at the contacting surfaces with the formation of a lubricating

tribolayer [19]. Thus, the higher wear loss of sialon com-

posite/steel couple in water lubrication, as observed in the

present case, could be linked to the mutual material transfer

and the formation of a non-protective hydrated silica layer.

8/18/2019 Lub Wear

7/11

 B. Basu et al. / Wear 250 (2001) 631–641   637

Fig. 5. Worn surfaces and EDS spectra of the tribolayers on the TiB2-based cermet with Ni3(Al, Ti) binder ((a) and (b)) and steel ball ((c) and (d)) after

fretting in water. EDS spectra are taken from the arrows indicated in the SEM micrographs. The arrow in (a) also indicates the embedding of the wear

debris on a rather smooth flat worn surface. The arrow in (c) implicates localized spalling of the tribochemical layer. The fretting direction is indicated

by a doubly pointed arrow.

Fig. 7 shows the surfaces in the ‘zirconia composite/steel’

wear couple after fretting in water. Red iron oxides are

occasionally found to stick to the wear scars on the zirconia

composite. The worn surface in the central part of the wear

pit on the composite was extremely smooth, as shown in

Fig. 7a, with iron oxide particles locally adhering to the TiB2phase. Only in these locations, Fe was detected with EDS

analysis (not shown). Mild abrasion marks due to the fret-

ting process could be observed optically (not shown). The

tribolayer on the steel ball was fragmented over the worn

steel surface, as shown in Fig. 7b. Compositional analy-

sis indicated that the tribolayer is a mixed oxide of Fe and

Cr with a small amount of dissolved Ti from the ceramic

(Fig. 7c). The experimental observations thus indicate that

TiB2   from the flat oxidizes, and transferred onto the steel

tribolayer. ZrO2  on the other hand was not observed to be

transferred onto steel worn surface, as could be expected

from literature [20]. The presence of rather low amount

(30 vol.%) of TiB2  phase and the stability of ZrO2  against

transfer to steel have resulted in limited tribochemical reac-

tions, compared to that observed with the other investigated

tribocouples. This, coupled with the mild abrasion marks on

the flat worn surface, corresponds well with the low fretting

wear rate of the ZrO2–TiB2  (70/30) composite against steel

in water.

3.2. Oil lubrication

3.2.1. Friction and wear data

In another set of experiments, the same TiB2-based ma-

terials were fretted against ball bearing steel in paraffin

oil under the same experimental conditions. When using

liquid paraffin as lubricating medium, a drastic reduction in

friction coefficient is observed for all the investigated fret-

ting couples (see Fig. 2b). The steady state friction values

for all the material combinations are in between 0.08 and

0.12. Comparing with the friction data observed under water

lubrication (see Section 3.1.1), it can be stated that paraffin

oil as compared to water is more efficient in reducing the

friction of the investigated materials against construction

steel.

After fretting in oil and subsequent ultrasonic cleaning,

the worn surfaces on the flats are observed to be very smooth

with an adhering tribofilm. Wear volume measurements

8/18/2019 Lub Wear

8/11

638   B. Basu et al./ Wear 250 (2001) 631–641

Fig. 6. Worn surfaces and EDS spectra of the tribolayers on the sialon–TiB2  composite ((a) and (b)) and steel ball ((c) and (d)) after fretting in water. Thearrow in (c) indicates the adherence of the tribolayer on the worn steel surface. The worn surface around the adhering tribolayer in (c) is predominantly

iron oxide. EDS spectra are taken from the arrows indicated in the SEM micrographs. The fretting direction is indicated by a doubly pointed arrow.

using a standard laser profilometer becomes impossible,

as the average depth of the wear pit is found to be com-

parable to the roughness of the flat surface. However, the

wear scars on the steel balls after fretting in oil could be

observed in the optical microscope and the wear volume is

evaluated from the geometry of the wear scar (see Fig. 3b).

The steel counterbody shows a higher wear volume in

contact with the TiB2

-based cermet. The wear volume

of the steel ball fretted against the monolithic TiB2   and

the sialon composite is comparable. The lowest wear is

measured when fretting was performed against zirconia

composite. It should be mentioned here that the volumet-

ric wear of the steel balls fretted in oil is reduced by two

orders of magnitude when compared to that under water

lubrication.

3.2.2. Morphological investigation of the worn surfaces

Fig. 8 illustrates the tribolayer formed on the worn sur-

face of the TiB2  monolith and steel ball after fretting in

liquid paraffin. The surface of the TiB2  material is hardly

worn and the abrasive scars are observed to be of the same

depth as the polishing marks on the native surfaces. The

worn surfaces on both flat and ball are covered by a thin

adherent tribofilm, as shown in Fig. 8a and b. The details

of the flat worn surface are shown in Fig. 8c. EDS analysis

(see Fig. 8d) of the tribolayer on the flat showed a strong

carbon peak along with an O peak. It is interesting to note

here that the tribocontact under oil lubrication is not com-

pletely free from the access to oxygen, as revealed by the

O peak. Additionally, EDS analysis showed the presence of 

Ti, B, and Fe on the worn surface. The amount of iron oxide

is considered small. The presence of Ti and B peak along

with an O peak indicates the oxidation of the TiB2  phase.

Oxidation of bulk TiB2  has been reported to start at 600◦C

in an oxidizing atmosphere [21], whereas it has been re-

vealed that the oxidation process of TiB2  in air starts even

below 400◦C, with the formation of TiBO3  [22]. However,

under the prevailing mechanical stress conditions during the

fretting tests, tribo-oxidation process can even start at much

lower temperature as often reported in the literature [23]. The

8/18/2019 Lub Wear

9/11

 B. Basu et al. / Wear 250 (2001) 631–641   639

Fig. 7. Worn surfaces of the ZrO2–TiB2  composite (a) and steel ball (b) after fretting in water. Note that the iron oxide particles are locally adhered to

TiB2, as pointed by an arrow in (a). The EDS spectrum (c) was taken from the tribolayer on the steel ball, as indicated by the arrow in (b). The fretting

direction is indicated by a doubly pointed arrow.

compositional analysis as reported above reveals that local

heating at the fretting contact, as also will be discussed be-

low, promoted the oxidation of the TiB2   phase in the oil

lubricated condition.

Since the microstructural analysis was carried out with-

out a conductive layer for SEM observation, the com-

positional analysis strongly indicates the formation of a

carbon-rich layer on the worn surface. The carbon de-

posit at the fretting contact could only be formed by the

tribodegradation-induced cracking of oil, which occurs at

500◦C [9]. The presence of carbon-rich tribolayer indicates

that the temperature generated locally at the fretting contact

in oil lubrication could be around or above 500◦C. Thus,

local heating and subsequent temperature rise in the contact

area is assumed to be the major cause for tribodegradation.

The carbon-rich layer serves as a lubricating third body,

reducing the friction and wear of the investigated tribosys-

tems. The same carbon deposit was observed on the surfaces

of the sialon–TiB2, the ZrO2–TiB2, and the TiB2-based

cermet composite as well as the steel counterbodies (not

shown) when fretted in paraffin oil.

The experimental results, presented in this work, are quite

significant for the selection of a suitable binder phase to de-

velop TiB2-based materials with improved fretting wear re-

sistance against steel in the lubricating media, distilled wa-

ter, and paraffin oil. Bulk TiB2

 phase from the flat oxidizes

during the fretting wear under the water lubricating medium

and tribochemically formed TiO2   is found to transfer onto

the tribochemical iron oxide layer. Both the sialon and in-

termetallic Ni3(Al, Ti) binder are also found to be oxidized

and incorporated into the tribolayer on steel via tribochem-

ical reactions. On the other hand, zirconia compared to the

other binders is not found to transfer onto worn steel surface.

Therefore, zirconia is assessed as the optimum binder for

TiB2-containing ceramics, which will offer the best fretting

wear resistance against steel. It should be noted here that

the amount of zirconia phase should be optimized, as with

increasing TiB2, the fretting wear rate of the tribosystem

8/18/2019 Lub Wear

10/11

640   B. Basu et al./ Wear 250 (2001) 631–641

Fig. 8. Overview of the worn surface on the TiB2  monolith (a) and steel ball (b) after fretting in paraffin oil with the details of the tribochemical layer

on the TiB2  material (c). The EDS spectrum (d) was taken from the tribolayer, as indicated by the arrow in (c). The fretting direction is indicated by a

doubly pointed arrow.

would increase through more tribochemical reactions and

transfer of the TiB2  phase onto steel.

4. Conclusions

1. The sialon composite/steel combination showed a higher

friction coefficient (0.48) than the other material com-

binations (COF   =   0.35–0.38) during the fretting tests

against steel in water. Significant reduction in friction

(COF around 0.08–0.12) when compared to that in water

for all the investigated materials against steel is observed

during the fretting tests in paraffin oil. Thus, liquid paraf-

fin is found to be the more effective lubricant than water

in reducing friction.

2. Under water lubrication, sialon–TiB2 /100Cr6 grade steel

couple is found to have the highest fretting wear rate,

whereas the zirconia composite/steel combination ex-

hibits the best fretting wear resistance among the inves-

tigated fretting couples. Wear data measured on the flats

do not follow any clear relationship with the mechanical

properties. The fretting wear of the flat materials after

testing in paraffin oil however is too low to be measured

with a standard laser profilometer.

3. Tribochemical reactions along with abrasion are the ma-

 jor mechanisms for fretting wear of investigated materials

against bearing grade steel in water. Both the sialon and

intermetallic binder have been observed to get oxidized

and transferred to the steel counterbody. TiB2 phase in all

the investigated materials is found to oxidize during the

fretting process and incorporated on the steel tribolayer.

8/18/2019 Lub Wear

11/11

 B. Basu et al. / Wear 250 (2001) 631–641   641

Zirconia, on the other hand, has not been found to trans-

fer on the steel counterbody. This along with mild abra-

sion marks on a smooth worn surface corresponds well

with the lowest fretting wear rate of ZrO2–TiB2  (70/30)

material.

4. The worn surfaces on all the investigated flats and balls

are found to be fully covered by the adherent carbon-rich(graphite) tribochemical lubricating layer after the fret-

ting tests in paraffin oil lubrication. Tribodegradation of 

the paraffin oil is found to be the major source for the car-

bon layer deposition. This observation corresponds well

with the significantly low friction and wear of the inves-

tigated tribosystems.

Acknowledgements

This work was supported by the Brite-Euram programme

of the Commission of the European Communities under

project contract no. BRPR-CT96-0304. The authors wouldlike to thank the University of Warwick, UK, and Centro de

Estudios e Investigaciones Técnicas de Guipúzcoa (CEIT),

San Sebastian, Spain, for the supply of the sialon–TiB2composites and TiB2-based cermets, respectively. B. Basu

thanks the Research Council of the Katholieke Universiteit

Leuven in Belgium for a research fellowship. The authors

also acknowledge the reviewers for the critical comments.

References

[1] W.M. Rainforth, Ceram. Int. 22 (1996) 365–372.

[2] R. Telle, Boride and carbide ceramics, in: R.W. Cahn, P. Haasen,E.J. Kramer (Eds.), Materials Science and Technology, Vol. 11:

Structure and Properties of Ceramics, VCH, Weinheim, 1994,

pp. 175–266.

[3] K.F. Dufrane, J. Am. Ceram. Soc. 72 (4) (1989) 691–695.

[4] S.M. Hsu, M.C. Shen, Wear 200 (1996) 154–175.

[5] S.W. Lee, S.M. Hsu, M.C. Shen, J. Am. Ceram. Soc. 76 (8) (1993)

1937–1947.

[6] J.D. Oscar Barceinas-Sanchez, W.M. Rainforth, J. Am. Ceram. Soc.

82 (6) (1999) 1483–1491.[7] B. Basu, R.G. Vitchev, J. Vleugels, J.-P. Celis, O. Van Der Biest,

Acta Mater. 48 (2000) 2461–2471.

[8] H. Liu, Q. Xue, Wear 201 (1996) 51–57.

[9] M. Kalin, J. Vizintin, S. Novak, G. Drazic, Wear 210 (1997)

27–38.

[10] M.F. Wani, B. Prakash, P.K. Das, S.S. Raza, J. Mukerji, Am. Ceram.

Soc. Bull. 76 (1997) 65–69.

[11] A.H. Jones, R.S. Dodeboe, M.H. Lewis, J. Eur. Ceram. Soc. 21 (7)

(2001) 969–980.

[12] F. Castro, I. Iturriza, J. Mater. Sci. Lett. 9 (1990) 600.

[13] B. Basu, J. Vleugels, O. Van Der Biest, A novel route to engineer

the toughness of Y-TZP ceramics, J. Eur. Ceram. Soc., submitted

for publication.

[14] H. Mohrbacher, J.P. Celis, J.R. Roos, Tribol. Int. 28 (5) (1995) 269–

278.[15] P.Q. Campbell, J.P. Celis, J.R. Roos, O. Van Der Biest, Wear 174

(1994) 47–56.

[16] D. Klaffke, Tribol. Int. 22 (2) (1989) 89.

[17] B. Basu, J. Vleugels, K.C. Hari Kumar R.G. Vitchev, O. Van Der

Biest, Unlubricated fretting wear of TiB2   containing composites

against bearing steel, Metallurg. Mater. Trans., submitted for

publication.

[18] T.E. Fischer, H. Tomizawa, Wear 105 (1985) 29–45.

[19] J. Takadoum, H.H. Bennani, D. Mairey, J. Eur. Ceram. Soc. 18

(1998) 553–556.

[20] J. Vleugels, O. Van Der Biest, Wear 225–229 (1999)

285–294.

[21] A. Tampieri, A. Bellosi, J. Mater. Sci. 28 (1993) 649–653.

[22] A. Kulpa, T. Troczynski, J. Am. Ceram. Soc. 79 (1996)

518–520.[23] I.L. Singer, MRS Bull. 6 (1998) 37–40.