friction and wear of titanium alloys sliding against metal, polymer, and ceramic counterfaces

9
Wear 258 (2005) 1348–1356 Friction and wear of titanium alloys sliding against metal, polymer, and ceramic counterfaces Jun Qu a,, Peter J. Blau a , Thomas R. Watkins a , Odis B. Cavin b , Nagraj S. Kulkarni a a Metals and Ceramics Division, Oak Ridge National Laboratory, P. O. Box 2008, MS 6063, Oak Ridge, USA b University of Tennessee, Knoxville, USA Received 11 July 2003; received in revised form 21 September 2004; accepted 23 September 2004 Available online 11 November 2004 Abstract Recent advances in lower-cost processing of titanium, coupled with its potential use as a light weight material in engines and brakes has renewed interest in the tribological behavior of titanium alloys. To help establish a baseline for further studies on the tribology of titanium against various classes of counterface materials, pin-on-disk sliding friction and wear experiments were conducted on two different titanium alloys (Ti–6Al–4V and Ti–6Al–2Sn–4Zr–2Mo). Disks of these alloys were slid against fixed bearing balls composed of 440C stainless steel, silicon nitride, alumina, and polytetrafluoroethylene (PTFE) at two speeds: 0.3 and 1.0 m/s. The friction coefficient and wear rate were lower at the higher sliding speed. Ceramic sliders suffered unexpectedly higher wear than the steel slider. The wear rates, ranked from the highest to the lowest, were alumina, silicon nitride, and steel, respectively. This trend is inversely related to their hardness, but corresponds to their relative fracture toughness. Comparative tests on a Type 304 stainless steel disk supported the fracture toughness dependency. Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analyses confirmed the tendency of Ti alloys to transfer material to their counterfaces and suggested possible tribochemical reactions between the ceramic sliders and Ti alloy disks. These reaction products, which adhere to the ceramic sliders, may degrade the mechanical properties of the contact areas and result in high wear. The tribochemical reactions along with the fracture toughness dependency helped explain the high wear on the ceramic sliders. © 2004 Elsevier B.V. All rights reserved. Keywords: Titanium; Ceramics; Material transfer; Tribochemical reaction 1. Introduction In comparison to light weight alloys based on aluminum and magnesium, titanium alloys present interesting possibil- ities as tribomaterials, but they have not been widely inves- tigated as bearing materials. They are harder and stiffer than Mg and Al alloys, and they resist exposure to heat and aque- ous corrosion much better. Like Al and Mg, their high affinity Research sponsored by the U.S. Department of Energy, Assistant Secre- tary for Energy Efficiency and Renewable Energy, Office of FreedomCAR and Vehicle Technologies, as part of the High Strength Weight Reduction Materials Program, under contract DE-AC05-00OR22725 with UT-Battelle, LLC. Corresponding author. Tel.: +1 865 574 4560; fax: +1 865 574 6918. E-mail address: [email protected] (J. Qu). for oxygen results in the formation of an adherent surface ox- ide, but sub-stoichiometric TiO 2 can act as a solid lubricant. A great deal is known about the physical metallurgy, heat treatment, and mechanical properties of titanium alloys, thanks to extensive aerospace-related research and develop- ment. Tribological concerns for Ti in aerospace components have focused mainly on their fretting behavior, leading to re- search on surface treatments like ion implantation and solid film lubrication [1,2]. Needs in the chemical process industry motivated a 1991 study of the galling and sliding wear be- havior of commercial-purity Ti and alloy Ti–6Al–4V [3]. In that investigation, the best wear and friction results for Ti al- loys were obtained for anodized counter-surfaces coated with MoS 2 solid-film or with polytetrafluoroethylene (PTFE), but the abrasion resistance was poor. Relatively few additional 0043-1648/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2004.09.062

Upload: jun-qu

Post on 02-Jul-2016

238 views

Category:

Documents


20 download

TRANSCRIPT

Page 1: Friction and wear of titanium alloys sliding against metal, polymer, and ceramic counterfaces

Wear 258 (2005) 1348–1356

Friction and wear of titanium alloys sliding against metal,polymer, and ceramic counterfaces�

Jun Qua,∗, Peter J. Blaua, Thomas R. Watkinsa, Odis B. Cavinb, Nagraj S. Kulkarnia

a Metals and Ceramics Division, Oak Ridge National Laboratory, P. O. Box 2008, MS 6063, Oak Ridge, USAb University of Tennessee, Knoxville, USA

Received 11 July 2003; received in revised form 21 September 2004; accepted 23 September 2004Available online 11 November 2004

Abstract

Recent advances in lower-cost processing of titanium, coupled with its potential use as a light weight material in engines and brakes hasrenewed interest in the tribological behavior of titanium alloys. To help establish a baseline for further studies on the tribology of titaniumagainst various classes of counterface materials, pin-on-disk sliding friction and wear experiments were conducted on two different titaniuma less steel,s re lower att ighest to thel eir relativf rgy dispersives faces ands dhere to thec s along witht©

K

1

aitMo

taML

ox-t.

rgy,lloys,velop-entsre-

solidstrybe-

i al-withut

ional

0d

lloys (Ti–6Al–4V and Ti–6Al–2Sn–4Zr–2Mo). Disks of these alloys were slid against fixed bearing balls composed of 440C stainilicon nitride, alumina, and polytetrafluoroethylene (PTFE) at two speeds: 0.3 and 1.0 m/s. The friction coefficient and wear rate wehe higher sliding speed. Ceramic sliders suffered unexpectedly higher wear than the steel slider. The wear rates, ranked from the howest, were alumina, silicon nitride, and steel, respectively. This trend is inversely related to their hardness, but corresponds to theracture toughness. Comparative tests on a Type 304 stainless steel disk supported the fracture toughness dependency. Enepectroscopy (EDS) and X-ray diffraction (XRD) analyses confirmed the tendency of Ti alloys to transfer material to their counteruggested possible tribochemical reactions between the ceramic sliders and Ti alloy disks. These reaction products, which aeramic sliders, may degrade the mechanical properties of the contact areas and result in high wear. The tribochemical reactionhe fracture toughness dependency helped explain the high wear on the ceramic sliders.

2004 Elsevier B.V. All rights reserved.

eywords:Titanium; Ceramics; Material transfer; Tribochemical reaction

. Introduction

In comparison to light weight alloys based on aluminumnd magnesium, titanium alloys present interesting possibil-

ties as tribomaterials, but they have not been widely inves-igated as bearing materials. They are harder and stiffer thang and Al alloys, and they resist exposure to heat and aque-us corrosion much better. Like Al and Mg, their high affinity

� Research sponsored by the U.S. Department of Energy, Assistant Secre-ary for Energy Efficiency and Renewable Energy, Office of FreedomCARnd Vehicle Technologies, as part of the High Strength Weight Reductionaterials Program, under contract DE-AC05-00OR22725 with UT-Battelle,LC.∗ Corresponding author. Tel.: +1 865 574 4560; fax: +1 865 574 6918.E-mail address:[email protected] (J. Qu).

for oxygen results in the formation of an adherent surfaceide, but sub-stoichiometric TiO2 can act as a solid lubrican

A great deal is known about the physical metalluheat treatment, and mechanical properties of titanium athanks to extensive aerospace-related research and dement. Tribological concerns for Ti in aerospace componhave focused mainly on their fretting behavior, leading tosearch on surface treatments like ion implantation andfilm lubrication[1,2]. Needs in the chemical process indumotivated a 1991 study of the galling and sliding wearhavior of commercial-purity Ti and alloy Ti–6Al–4V[3]. Inthat investigation, the best wear and friction results for Tloys were obtained for anodized counter-surfaces coatedMoS2 solid-film or with polytetrafluoroethylene (PTFE), bthe abrasion resistance was poor. Relatively few addit

043-1648/$ – see front matter © 2004 Elsevier B.V. All rights reserved.oi:10.1016/j.wear.2004.09.062

Page 2: Friction and wear of titanium alloys sliding against metal, polymer, and ceramic counterfaces

J. Qu et al. / Wear 258 (2005) 1348–1356 1349

Table 1Compositions and characteristics of Ti–6Al–4V and Ti–6Al–2Sn–4Zr–2Mo

Ti alloy Compositions (wt%)* (balance Ti) Microindentation hardness HV (GPa) Tensile strength UTS (MPa)

Ti64 6.53 Al, 3.89 V, 0.13 Fe 3.36± 0.17 954.9Ti6242 5.85 Al, 1.98 Sn, 4.22 Zr, 1.95 Mo 3.31± 0.10 957.0

∗ Analyses supplied by Titanium Metals Corporation.

studies have been conducted on sliding wear mechanisms ofTi alloys. Molinari et al. highlighted the mechanisms respon-sible for the wear resistance under different load and slidingspeed conditions in self-mated Ti–6Al–4V disk-on-disk slid-ing tests[4], and Dong and Bell[5] reported unexpectedlyhigh wear rates for alumina sliding against Ti–6Al–4V (pin-on-disk tests).

Recent developments in Ti processing forecast the avail-ability of lower-cost Ti and that has prompted further interestin exploring the tribological behavior of Ti alloys as bearingmaterials[6]. Focus by the U.S. Department of Energy on im-proved brake materials for fuel-efficient heavy trucks, has ledto the consideration of Ti for disc brake rotors as well. In fact,coated Ti brake discs are already showing promise in auto rac-ing [7]. This renewed interest in the friction and wear of Tialloys has prompted the current laboratory study of the behav-ior of two commercially-available Ti alloys sliding againstmodel metallic, ceramic, and polymeric counterfaces. Oneof the two alloys (Ti–6Al–4V) has had more tribological at-tention than the other, but the other (Ti–6Al–2Sn–4Zr–2Mo)has attractive elevated temperature properties and was feltto be of interest as well. There are very few studies on thetribological properties of Ti–6Al–2Sn–4Zr–2Mo in the liter-ature. In this study, it is intended to establish baseline data forthese alloys with which to compare the tribological behavioro

2

–4 bse-q tions

uctures

of these alloys, provided by the supplier for these heats of ma-terial, are listed inTable 1and their microstructures are shownin Fig. 1(a) and (b), respectively. The typical�, �/�-phasegrain structure can readily be identified on the etched cross-section of Ti64. Ti6242 has finer grain size and is dominatedby �-phase. The two alloys have similar microindentationhardness and tensile strength (seeTable 1).

Friction and wear tests were conducted using a pin-on-diskapparatus. The diameter of the fixed ball sliders was 9.53 mm.As shown inTable 2, 440C stainless steel, silicon nitride, alu-mina, and polytetrafluoroethylene (PTFE), were selected torepresent metallic, ceramic, and polymeric bearing materials.The Ti alloy disks were 63.5 mm diameter and 12.7 mm thick.The disk surfaces were polished by 600 grit wet SiC abrasivepaper and the pre-test arithmetic average surface roughness(Ra), measured with a Taylor Hobson TalysurfTM 10 stylusprofilometer with a 2.5�m tip radius, was 0.11± 0.02�m.Concentric wear tracks ranging from 18 to 52 mm in diameterwere used, and the disk rotation rate was adjusted accordinglyto provide either 0.3 or 1.0 m/s sliding speed. A 10 N normalload was applied and the test was run for 500 m sliding dis-tance. In follow-on experiments, and to provide a comparisonto the results for the Ti alloy disks, a 304 stainless steel disk(63.5 mm diameter and 6.35 mm thick) was tested against440C stainless steel and ceramic (Si3N4 and Al2O3) slid-e tionV bout3

sedf lidersa entsw s thew ding

f new surface treatments or coatings in future work.

. Materials and testing procedure

Two titanium alloys, Ti–6Al–4V and Ti–6Al–2SnZr–2Mo, were tested in this study. These alloys shall suuently be referred to as Ti64 and Ti6242. The composi

Fig. 1. Microstr

of two Ti alloys.

rs under similar sliding conditions. The microindentaickers hardness of the 304 stainless steel disk was a.16 GPa, slightly lower than that of the Ti alloy disks.

The friction force was monitored by a load cell-baorce measurement system. The wear volumes of the snd disks were determined by weight change measuremith an accuracy of 0.1 mg. The wear factor is defined aear volume normalized by the applied load and the sli

Page 3: Friction and wear of titanium alloys sliding against metal, polymer, and ceramic counterfaces

1350 J. Qu et al. / Wear 258 (2005) 1348–1356

Table 2Characteristics of slider materials

Sliders Supplier Specification Vickers hardness (GPa) Fracture toughness (MPa m1/2)

440C stainless steel McMaster-Carr Grade 100 Hardened 12.60a 23.7b

Silicon nitride Cerbec East Granby, CT NBD200 Grade 5 19.37a 5.2c

Alumina Southern Bearing Service AFBMA Grade 25 24.75a 3–4c

PTFE W.M. Berg, Inc. East Rockaway, NY – N/A N/Aa The Vickers hardness was measured using a 100 g load.b The Izod impact strength of hardened 440C stainless steel is 4 ft lb[8]. The fracture toughness here was estimated based on Barsom–Rolfe’s empirical

formula[9], with the assumption that the Izod impact strength is close to the Charpy V-notch impact strength.c The fracture toughness values were provided by the suppliers.

distance of the pin. All the tests were conducted in ambientair conditions with temperature and humidity in the rangeof 18–22◦C and 52–62%, respectively. At least two dupli-cates were run at each test condition. Good repeatability wasobtained in both friction and wear results.

3. Results

Results are summarized inTable 3(a) and (b) for Ti64 andTi6242, respectively. Friction and wear results are presentedseparately.

3.1. Friction

Table 3(a) and (b) present the average friction coeffi-cient and its fluctuation at steady-state for each test con-dition. Selected friction traces of the four different slidersagainst Ti64 disks are shown inFig. 2. The PTFE slider gen-erated a fairly smooth friction trace (Fig. 2(d)) due to itsself-lubricating nature. The metal and ceramic sliders pro-duced friction coefficient in the range of 0.34–0.50 with rel-atively large fluctuation, as illustrated inFig. 2(a)–(c). The

TF

S

/N m)

Disk

(1.7×3.5×5.7×N/Ma

(1.3×3.5×3.4×N/Ma

large fluctuation of the friction coefficient was thought tobe caused by formation and periodic, localized fracture ofa transfer layer. Titanium alloy commonly transfers to thecounterface when rubbing against other metals or ceramics[3–5]. In this study, surface morphology examination andsurface analysis confirmed this tendency. A transfer layerwas easily identified on the wear scar of the 440C stain-less steel ball (seeFig. 3(a)). The energy dispersive spec-troscopy (EDS) analysis detected Ti and/or Al on the wornsurfaces of the metal and ceramic balls, as shown inFig. 4.More discussion on surface analysis can be found on Section4.2.

For metal and ceramic balls, lower friction coefficient andsmaller instantaneous fluctuation were observed at 1.0 m/scompared to those at 0.3 m/s, as shown inTable 3. At highersliding speed, the contact area had higher temperature, whichgenerally reduced the shear strength and led to lower frictionforces.

3.2. Wear

As shown inTable 3(a) and (b), up to five times higher wearfactors were obtained on both the slider and disk at 0.3 m/s

able 3riction and wear results

lider material Sliding speed

0.3 m/s

Friction coefficient Wear factor (mm3

Ball

a) Ti–6Al–4V disks440C stainless steel 0.50± 0.05 6.9× 10−6

Silicon Nitride 0.47± 0.07 3.8× 10−5

Alumina 0.49± 0.07 5.7× 10−5

PTFE 0.28± 0.001 8.4× 10−4

b) Ti–6Al–2Sn–4Zr–2Mo disks440C stainless steel 0.48± 0.05 5.1× 10−6

Silicon nitride 0.47± 0.08 4.4× 10-5

Alumina 0.49± 0.08 1.2× 10−4

PTFE 0.27± 0.001 9.9× 10−4

a N/M, not measurable.

1.0 m/s

Friction coefficient Wear factor (mm3/N m)

Ball Disk

10−4 0.35± 0.05 1.6× 10−6 1.5× 10−4

10−4 0.36± 0.07 6.2× 10−6 1.3× 10−4

10−4 0.44± 0.07 1.6× 10−5 2.0× 10−4

0.29± 0.001 6.1× 10−4 N/Ma

10−4 0.34± 0.04 1.22× 10−6 1.1× 10−4

10−4 0.37± 0.02 9.40× 10-6 1.1× 10−4

10−4 0.42± 0.04 2.33× 10−5 2.2× 10−4

0.29± 0.001 7.92× 10−4 N/Ma

Page 4: Friction and wear of titanium alloys sliding against metal, polymer, and ceramic counterfaces

J. Qu et al. / Wear 258 (2005) 1348–1356 1351

Fig. 2. Frictional traces of different sliders against Ti64 disks.

than those at 1.0 m/s. Similar sliding speed dependency wasalso reported by other researchers[5].

The Ti disks suffered high wear rates, in the order of10−4 mm3/N m, against the metal and ceramic balls, andharder sliders generated relatively more (or at least compara-ble) wear on the Ti disks. Although harder balls were expectedto have higher wear resistance, the results inTable 3(a) and(b) show a reverse order: the alumina ball wore more than thesilicon nitride ball, which in turn wore more than the stainlesssteel ball. Remarkably, the wear factors of the ceramic ballswere at least five times higher than those of the steel balls.Dong and Bell also reported a higher wear rate of an aluminaball than that of a steel ball when sliding against a Ti64 disk[5]. More analysis and discussion are presented in Section4.

Fig. 3 shows the wear scars on the metal and ceramicballs with features of abrasive wear, adhesive wear, and plas-tic deformation. Abrasive wear seemed to dominate the wearprocess at 0.3 m/s. Those wear scars were larger and flatter,corresponding to their higher wear factors. The wear scarsgenerated at 1.0 m/s were smaller but much rougher withlarger patches of transferred material implying more severeadhesive wear, possibly due to higher temperature at the con-tact area. EDS analysis also showed higher Ti and/or Al con-centration on the wear scars at 1.0 m/s.

The PTFE slider had the highest wear factor( −3 3 o-

tected by the polymeric layer transferred from the PTFEball and had almost no surface damage except a few shallowcircular groves ground by third body particles, probablysome metal debris, embedded in the PTFE ball.

It has been seen that these two Ti alloys showed simi-lar friction and wear behavior. Therefore, discussion will befocused on Ti64 only.

4. Discussion

The most unusual finding of this study was the observa-tion that the relatively hard ceramic sliders wore considerablymore severely than the softer stainless steel slider. Mechan-ical and chemical analyses have been conducted to try toexplain these results.

4.1. Fracture toughness

The wear resistance of 440C stainless steel, silicon car-bide, and alumina pins is in the reverse order as their relativeVickers hardness numbers, but in the same relative order astheir fracture toughness.

Recognizing that the current work was on sliding wear, theabrasive wear of ceramics has been proposed to be a functiono s

10 mm /N m). Its counterface (Ti disk) was pr f both hardness and fracture toughness[10]. Further studie
Page 5: Friction and wear of titanium alloys sliding against metal, polymer, and ceramic counterfaces

1352 J. Qu et al. / Wear 258 (2005) 1348–1356

Fig. 3. SEM images of wear scars on the balls sliding against Ti64 disks.

on ceramic wear mechanisms showed that fracture toughnessmay play a dominating role in wear resistance. For example,Fischer[11] has demonstrated that, in the case of yttria sta-bilized zirconia ceramics, the wear resistance increases withthe fourth power of fracture toughness.

The pin-on-disk apparatus is mainly intended to evaluatesliding wear, but in practice, the load history can consist of

sliding and impact, since vibrations may occur if the disksurface is not perfectly normal to the axis of rotation. Thetendency for impact to occur for small errors in alignmentdepends also on the sliding speed and how far the contactis from the center of rotation. Unlike sliding that usuallycauses plastic shearing in materials, impact may introducecatastrophic failures, such as cracking and crushing of the

Page 6: Friction and wear of titanium alloys sliding against metal, polymer, and ceramic counterfaces

J. Qu et al. / Wear 258 (2005) 1348–1356 1353

Fig. 4. EDS analysis of the wear scars on the sliders.

contact surfaces, leading to faster material removal and theproduction of sharp ceramic debris fragments that can in turncause three-body abrasion. Brittle materials, like ceramics,are more sensitive to such repeated impact effects than aretougher metals. Rice et al.[12,13]have studied the wear rateand mechanism of compound impact (impact and sliding)on metals and superalloys. The material with lower fracturetoughness had a higher wear rate and gave strong evidencefor subsurface damage.

To test the dependency of the wear rate on fracture tough-ness, comparative tests were conducted on a 304 stainlesssteel disk sliding against the 440C stainless steel, silicon ni-tride, and alumina sliders, under 10 N load and at 0.3 m/sspeed for 500 m. Friction and wear results for the 304 stain-less steel disk are shown inTable 4. The alumina, siliconnitride, and 440C stainless steel balls had the wear rate fromhigh to low. This confirmed the fracture toughness effect.However, it has been noticed that the sliders against the steel

Table 4Friction and wear results for 304 stainless steel disks against metal andceramic sliders

Slider material Friction coefficient Wear factor (mm3/N m)

Ball Disk

440C stainless steel 0.55± 0.05 <1× 10−6 2.52× 10−4

Silicon nitride 0.68± 0.08 1.15× 10−6 2.01× 10−4

Alumina 0.57± 0.03 9.80× 10−6 5.41× 10−4

disk had much lower wear factors than those against the Tidisks at the same testing condition (seeTables 3 and 4), whilethe 304 stainless steel and Ti64 disks had similar hardness andcomparable wear factors. This suggests that there might beother sources influencing the wear rate.

4.2. Tribochemical reactions

It is known that mechanically deformed surfaces usu-ally have different chemical reactivity than purely thermallystressed solids[14]. Tribochemical reactions may signifi-cantly accelerate the wear process. Surface analyses (EDSand XRD) were conducted on the contact surfaces to explorethe possibility of tribochemical reactions that may inducethe unexpected high wear rates on the ceramic sliders.Fig. 4shows the EDS spectra of the wear scars on the balls that slidagainst the Ti64 disks. The EDS analyses indicated Ti andAl on the worn surfaces of the steel and alumina balls (seeFig. 4(a) and (c)), which indicate material transfer from theTi64 disk to the sliders. It is interesting to notice that only Albut no Ti was found on the wear scar of the silicon nitride ball(seeFig. 4(b)). No Al was observed on the unworn region ofthis ball. This may imply that the detected Al was probablynot in metallic form (otherwise Ti should be present too), buthad chemical compounds with other elements, such as Si, O,a

earswt mo dis-pt d bys arsiD ride( ,t ility.A risf noi be-c y off on-m idesw were

nd/or N present inFig. 4(b).X-ray diffraction was then used to further analyze the w

cars on the ceramic sliders. A four-axis goniometer[15]as employed for the grazing incidence (2◦) X-ray diffrac-

ion measurements using Cu K� radiation and parallel beaptics. That technique eliminates the sample surfacelacement errors due to the spherical shape.Fig. 5 shows

he XRD patterns of the wear scar and debris generateilicon nitride against Ti64.Fig. 5(a) reveals that the wecar on the silicon nitride ball contains silicon nitride (Si3N4)n both �- and�-phase and silicon oxide nitride (Si2N2O).ue to the peak superposition, silicon aluminum oxide nit

Si5AlON7) cannot be distinguished from Si3N4. Howeverhe presence of Al detected by EDS supports this possibs shown inFig. 5(b), the XRD analysis on the wear deb

ound titanium, silicon nitride, and titanium nitride, butndication of titanium oxides. This was a little surprisingause titanium oxides have the lower Gibbs free energormation than the titanium nitride in the ambient envirent. One possible explanation is that the titanium oxere amorphous due to severe plastic deformation and

Page 7: Friction and wear of titanium alloys sliding against metal, polymer, and ceramic counterfaces

1354 J. Qu et al. / Wear 258 (2005) 1348–1356

Fig. 5. X-ray diffraction analysis of the wear scar and debris for silicon nitride sliding against Ti64.

not detected by XRD. The XRD pattern of the worn sur-face on the alumina ball sliding against a Ti64 disk is shownin Fig. 6. The observed spinel (MgAl2O4) was probably asintering aid. The XRD pattern may suggest some possibil-ity of forming titanium–aluminum intermetallic compounds(Al3Ti, Al 2Ti), but there was no strong evidence. Titaniumaluminides were also suspected by Dong and Bell[5] based

on the XRD analysis of the wear debris produced by aluminasliding against Ti64.

The high wear rates of alumina and silicon nitride slid-ers may be attributed to the formation of chemical reac-tion products between them and the Ti and/or Al transferredfrom the Ti64 disks. Such tribochemical reactions were alsoaided by the lower thermal conductivity of Ti that promotes

Page 8: Friction and wear of titanium alloys sliding against metal, polymer, and ceramic counterfaces

J. Qu et al. / Wear 258 (2005) 1348–1356 1355

Fig. 6. X-ray diffraction pattern of the wear scar on the alumina slider against the Ti64 disk.

a higher temperature near the interface. These reaction prod-ucts bonded to the ceramic contact surfaces may deterioratetheir mechanical properties and result in micro fractures lead-ing to high wear. The wear process continuously developed“fresh surfaces” and in turn accelerated the tribochemical re-actions.

5. Summary

The tribological behavior and responsible wear mech-anisms for titanium alloys Ti–6Al–4V and Ti–6Al–2Sn–4Zr–2Mo, sliding against 440C stainless steel, silicon nitride,alumina, and PTFE were investigated. The following obser-vations and conclusions were obtained:

(1) The two Ti alloys had similar friction and wear perfor-mance, although their grain structures and compositionsare different.

(2) Large frictional fluctuations occurred when metal andceramic balls slid against Ti alloy disks, probably causedby formation and periodic, localized fracture of a transferlayer.

(3) Higher friction coefficient with larger fluctuation andhigher wear rate were observed at the lower sliding speed.

(4) Despite their higher hardness, ceramic sliders experi-n the

( haveratestain-

less steel disk supported the fracture toughness depen-dency of the wear rate.

(6) EDS and XRD analyses confirmed material transfer fromthe Ti alloy disks to their counterfaces and suggestedpossible tribochemical reactions.

Acknowledgements

The authors with to acknowledge with appreciation Y.Kosaka of Titanium Metals Corporation, USA, for supply-ing alloy billets along with their chemical analyses. Supportfor this research was provided by the U.S. Department ofEnergy, Assistant Secretary for Energy Efficiency and Re-newable Energy, Office of FreedomCAR and Vehicle Tech-nologies, as part of the High Strength Weight Reduction Ma-terials Program, under contract DE-AC05-00OR22725 withUT-Battelle, LLC. J. Qu and N. Kulkarni were supported inpart by appointments to the ORNL Postdoctoral Research As-sociates Program administered jointly by ORNL and ORISE.

References

[1] F.M. Kustas, M.S. Misra, Friction and wear of titanium alloys, in:ear

the

rials,

enced much higher wear and created more wear ocounterfaces than did the stainless steel sliders.

5) Fracture toughness and tribochemical reactionsbeen proposed to explain the unexpected high wearon the ceramic sliders. Comparative tests on a 304 s

P.J. Blau (Ed.), ASM Handbook, Friction, Lubrication, and WTechnology, 18, ASM International, 1992, pp. 778–784.

[2] R.B. Waterhouse, A. Iwabuchi, The effect of ion implantation onfretting wear of four titanium alloys at temperatures up to 600◦C, in:Proceedings of the International Conference on Wear of MateASME, New York, 1985, pp. 471–484.

Page 9: Friction and wear of titanium alloys sliding against metal, polymer, and ceramic counterfaces

1356 J. Qu et al. / Wear 258 (2005) 1348–1356

[3] K.G. Budinski, Tribological properties of titanium alloys, Wear 151(1991) 203–217.

[4] A. Molinari, T.B. Straffelini, T. Bacci, Dry sliding wear mechanismsof the Ti6Al4V alloy, Wear 208 (1997) 105–112.

[5] H. Dong, T. Bell, Tribological behavior of alumina sliding againstTi6Al4V in unlubricated contact, Wear 225–229 (1999) 874–884.

[6] EHKT Technologies, Opportunities for low cost titanium in re-duced fuel consumption, improved emissions, and enhanced dura-bility heavy-duty vehicles, Oak Ridge National Laboratory Report,ORNL/Sub/4000013062/1, Oak Ridge, Tennessee, 2002, p. 59.

[7] Ultra-Lite Brakes and Components, Literature, Red Devil Brakes,Inc., Mt. Pleasant, Pennsylvania, not dated.

[8] S. Lampman, Fatigue and fracture properties of stainless steel, in:S.R. Lampman (Ed.), ASM Handbook, Fatigue and Fracture, 19,ASM International, 1996, pp. 712–732.

[9] J.M. Barsom, S.T. Rolfe, Correlations between KIC and Charpy V-notch test results in the transition temperature range, in: Impact

Testing of Materials STP 466, ASTM, Philadelphia, 1979, pp. 281–302.

[10] A.G. Evans, D.B. Marshall, Fundamentals of Friction and Wear ofMaterials, ASM, 1980, p. 439.

[11] T.E. Fischer, Friction and wear of ceramics, Scripta Metall. Mater.24 (1990) 833–838.

[12] S.L. Rice, The role of microstructure in the impact wear of twoaluminum alloys, ASME Proc. Wear Mater. (1979) 27–34.

[13] S.L. Rice, H. Nowotny, S.F. Wayne, Characteristics of metallic sub-surface zones in sliding and impact wear, ASME Proc. Wear Mater.(1981) 47–52.

[14] G. Heinicke, Tribochemistry, Carl Hanser Verlag Munchen Wien,Berlin, 1984.

[15] H. Krause, A. Haase, X-Ray Diffraction System PTS for Powder,Texture and Stress Analysis, in: H.J. Bunge (Ed.), ExperimentalTechniques of Texture Analysis, vol. 405–408, DGM Informations-gesellschaft, Verlag, 1986.