382 Surface Treatment, Computer Methods and ......Wear behaviour of plasma sprayed TiC-15%Ni...

$: 382 Surface Treatment, Computer Methods and ......Wear behaviour of plasma sprayed TiC-15%Ni coatings R. J. C. Cardoso*, M. A. Ashworth\ M. H. Jacobs* ^Department of Science and Technology$
Wear behaviour of plasma sprayed TiC-15%Ni

coatings

R. J. C. Cardoso*, M. A. Ashworth\ M. H. Jacobs*

^Department of Science and Technology of Materials, The Federal

University of Bahia, RuaAristides Novis, 2, Federagao, Salvador,

in Materials for High Performance Applications. The

University of Birmingham, England, U.K., B15 2TT.

Email [email protected]

Abstract

Wear resistance properties of TiC reinforced Ni thermally sprayed coatings have beeninvestigated. The powder used was nickel coated titanium carbide particles (TiC-15%Ni), size: -106+45 Jim. The starting powder was characterized via metallography, SEM and X-raydiffraction analysis for identification of its morphology and the phases present. The TiC-15%Nipowder was then deposited on to AISI 1019 carbon steel substrates (60 mm dia. and 10 mmthick wear discs) using an APS (Air-Plasma-Spray) Plasma Technik gun. The plasma gunproduced a plasma jet as a result of ionization of Ar/H gas mixture. The structure of the coatingswere studied by optical microscopy and the phases were determined with X-ray diffraction. Also,the microhardnesses of the coatings were measured. The results for TiC-15%Ni coatings werecompared to those obtained for a standard WC-12%Co (ANDRY 301) coating as deposited byAPS. A ball-on-disc wear testing method was employed to evaluate all material coatings underunlubricated and room temperature sliding wear conditions. The results include wear volumesand coefficients of friction.

TiC- 15% Ni coatings had a structure of high porosity, lower values of hardness andcoefficient of friction when compared to the corresponding values of WC-12% Co. The X-raydiffraction (XRD) patterns of the starting powder and plasma sprayed TiC- 15% Ni coatingsconsisted only of TiC and Ni phases. The results of volume loss for TiC- 15% Ni coatingsdeposited by atmospheric plasma spraying were higher than the WC-12% Co sprayed coatings.TiC reinforced metal powder coatings studied here promise to provide a lower coefficient offriction and better wear performance in coatings of lower porosity. Certain applications maybenefit from these attributes.

1 Introduction

Wear is recognised as a serious problem in many areas of industry/ '. Coatingstechnologies have steadily gained in importance in response to the need toconserve expensive materials by replacement with cheaper substrates whosesurfaces are enhanced to withstand the required conditions of service. Coatingtechnology is an important enabling manufacturing process that could permitmany industrial companies to enhance their competitiveness and, henceprofitability significantly. Cobalt-based thermal spray deposits with additions of

Transactions on Engineering Sciences vol 17, © 1997 WIT Press, www.witpress.com, ISSN 1743-3533

382 Surface Treatment, Computer Methods and Experimental Measurements

tungsten carbide, from Co-WC powders, are used widely in Europe and Americaas wear resistant coatings. Alternative deposits with similar or better technicalperformance, under specific conditions, coupled with either processingadvantages and/or cost benefits, would be of appreciable interest.

Carbide reinforcement of metals has been used as a successful technique forimproving the wear resistance of surfaces/"*. These materials are known as"Ceremets" and the idea is combine ceramic phases with metallic matrices in orderto produce materials with superior properties to those attained with ceramics ormetals independently/. To a first approximation, the hard carbide particlesprovide resistance to abrasion, whereas the matrix confers cohesion andtoughness. The first generation of ceremets appeared after publication of theSchroter patent covering WC-CO hard metals A

Since the late 1950s, thermal spray techniques have been shown to be asuccessful method for depositing coating surfaces,". Carbide particles such asWC, or Cr^Cy and TiC have proved to be effective when added to tougher, moreductile binder matrices/. WC or Cr^C reinforced materials, are used in manyapplications to decrease sliding or erosive wear. TiC reinforced materials,however, produce a lower weight and a superior temperature wear resistantcoating,*. If TiC phase is stable and well bonded and dispersed into the matrix, ahard, low coefficient of friction surface is produced. Recently, there have beenmany studies on TiC reinforced metal/" . These works show that the coatingsmade from TiC reinforced powders, are more resistant to sliding wear than eitherWC/Co or Stellite,'-. This type of carbide has been selected due to its lowerweight, higher compatibility, and its lower friction coefficients. Compared totungsten carbide and chromium carbide based coatings, titanium carbide particlebased coatings have a lower weight and superior high temperature behaviour.

Cr Cy or WC may decompose at higher operating temperatures and would notprovide the equivalent low friction coefficient. WC or W%C tend do decomposepartially at temperatures higher than 540°C over long term.

The present study was conducted to evaluate the wear behaviour of thermalsprayed TiC-15%Ni, which is a cobalt-free system and which was comparedwith a thermal sprayed tungsten carbide cobalt, WC-Co coating. The startingpowders and spray coatings were tested and characterized via metallography,SEM and X-ray diffraction analysis for identification of their morphologies andthe phases present. Microhardness testing (Vickers, 300 g load) and ball-on-discwear testing were carried out on all materials, which yielded results that includedwear volumes and coefficients of friction.

2 Experimental Procedures

Powder Manufacturing: The spray powder used in this study was TiC-15%Nipowder in which TiC-particles was coated with nickel. The particles size

distribution of the powder is -106+45 |im. This powder was supplied by London& Scandinavian Metallurgical Co. Limited and the other two powders weresupplied from ANDRY, as given in Table 1.

Deposition Processes: Plasma gun spraying was performed at the IRC inMaterials for High Performance Applications at The University of Birmingham,UK. The powders shown in Table 1 were deposited using an Air Plasma Spray -APS process. Plasma spraying was performed with the Plasma-Technik-AG gun,using argon and hydrogen as plasma gases for all coatings. The main sprayparameters used are presented in Table 2. Two layers, a bond coat followed by atrial coating, were deposited on a rolled mild steel (AISI 1019) 50 mm dia. X 10mm thick wear discs. All the discs were grit blasted with 500 microns alumina


Surface Treatment, Computer Methods and Experimental Measurements 383

(AUOO particles and ultrasonic ally cleaned in methanol prior to spraying. A bondcoat of Al-5%Ni powder was the first layer deposited on to all specimens. Thepowders particles were injected internally into the plasma jet environment, wherethey melted and accelerated towards a moving substrate. The powders wereconsolidated onto discs. Nominal coatings thickness on wear discs were 0.25mm.

PowderReference

1

2

3

Composition

Ni-85%v.TiC

Ni-5%Al

WC-12%Co

ManufactureMethod

Agglomerated

Spheroidal/GranularNi clad with Al

Fused and crushed

Comments

-106+45 jamANDRY 956

-90+45 |imANDRY 301

Table 1. Powder Compositions.

Powder

123

Arc gas 1(1/min)

Ar/65Ar/45Ar/65

Arc gas 2(1/min)

H/9.5H/llH/3

Carriergas

(1/min)Ar/3.5Ar/3.3Ar/2

Powderfeed rate(g/min)506036

Current(A)

600600700

Spraydistance(mm)100140130

Table 2 . Process Parameters and Spray Conditions.

Characterization and Testing: Characterization and coating property tests wereconducted on the TiC-15%Ni powders and all coated specimens. The TiC-15%Nistarting powder was characterized via SEM analysis to identify its morphologyand X-ray diffraction (XRD) was performed for identification of the phasespresent. Microhardness tests, metallographic evaluation, wear properties and X-ray diffraction were conducted on the plasma coated test discs.

The sprayed coatings were grounded up to 120 mesh SiC paper.Microhardness measurements (Vickers diamond indentor at 300 g load) wereperformed on the coated surfaces; twelve (12) values were recorded and anaverage was taken. X-ray diffraction patterns were obtained from the coatedsurfaces with a Dyane diffractometer, in order to identify the phases present andthen relate them to the features observed by optical and scanning electronmicroscopy

Friction and wear tests on the coatings were performed at room temperaturewith a pin-on-disc tribometer. Sliding ball-on-disc tests were conducted on eachcoated disc under unlubricated (dry) conditions. The test pair used was Co-WCballs, 6 mm in diameter as counter body. The coated discs, 50 mm in diameter,10 mm thick, ground to an average surface roughness of 5 micron. The testswere conducted at 23 mm track diameter and 125 rpm, giving a surface speed of0,30 m/sec. A 23 N load was used in all tests. Each test was carried out for a totalof 5,000 cycles. The frictional forces and coefficient of friction values werecontinuously recorded on a computer and sampled at a frequency of 1 Hz. Theball -on-disc wear test set-up is shown schematically in Figure 1. Wear-volumemeasurements on the coatings, at the end of each test, were made by calculatingthe area of the wear track from a profile trace measured by a surface profilometer.



Environment

r applied 1 Coalingcompositionstructure

Test Measurtmtnts

Wear Track- rpm- time / cydea- diameter

Fig. 1 Schematic presentation of sliding wear test: pin-on-disc (POD) apparatus.

a) 150X b) 350X

Fig. 2 SEM micrographs of the TiC-15% Ni agglomerated powder.



Powder section 400X; Powder section 850X.

Fig. 3 SEM micrographs of the TiC-15% Ni agglomerated powder. The lightphase is nickel and the grey phase is TiC.

*#__'

a) TiC-15%Ni coating b) WC-12%Co coating

Fig. 4 Optical microstructures of APS sprayed coatings, as polished (x200).



The average wear cross sectional area were then multiplied by the circumferenceof the wear track to obtain the wear volume.

3 Results and Discussion

Powder characterization: Fig. 2 shows SEM micrographs of the TiC-15% Niagglomerated powder as supplied by London & Scandinavian Metallurgical Co.Limited. The Fig. 3 shows a cross section of a particle of powder. The lightphase is nickel and grey phase is TiC. The X-ray diffraction patterns of thestarting powder are shown in Fig. 5 (a), which revealed the TiC particles and Niphase.Hardness: the microhardness results of the TiC-15% Ni and WC-12% Co plasmasprayed coatings are shown in Table 3. The microhardness value of the sprayedTiC-15% Ni coatings was 603 HV/0.3 Kg. It is remarkably lower than thecorresponding value of 824 HV/0.3.Kg obtained for WC-12% Co coatings.

Nominal thickness ( Jim )Microhardness Vickers ( 300 g )Wear resistance/Loss of volume (mnf )Coefficient of friction ( COF )

Average roughness Ra (|im )

TiC-15% Ni250

6032.70.4074.0

WC-12%250

824(*)0.6415.0

Co

( * ) No volume loss was detected on the coatings

Table3. As-sprayed Coating Properties

Microstructure: The optical micrographs of the TiC-15% Ni and WC-12% Coplasma sprayed coatings are presented in Fig. 4. The micrograph (a) shows ahigh level of porosity and unmelted particles of powder for TiC-15% Ni coatings.Deposit evaluations have not shown acceptable densities of all TiC reinforcedmaterials with plasma conditions given in Table 2. Possibly coarse powder ofTiC-15% Ni materials were not effectively melted by the Ar/H jet conditions usedand lower deposit densities resulted. The lower results of hardness for TiC 15%Ni coatings can be correlated to the high porosity revealed in micrograph Fig. 4(a). The WC-12% Co coatings display a structure much more dense as seen inFig. 4(b).

Wear result: Wear volumes and coefficients of friction for all tested coatings aredisplayed in Table 3. The volume loss values show that the coatings made fromTiC-15% Ni alloys ( 2,7 mnf ) were higher as those of WC-12% Co coatings,which were negligible. No wear track was detected by profilometer on WC-12%Co coatings. After each wear test on WC-12% Co coatings, the Co-WC ballswere visibly worn. The lower wear performance for TiC reinforced Ni coatingsmay be related to the high porosity of the TiC-15% Ni coatings. The Table 3shows that the coefficient of friction - COF values for TiC-15% Ni coatings areslightly lower than the WC-12% Co coatings. However, it is very hard tocorrelate coefficient friction (COF) with any other properties of the coating.

X-Ray Diffraction: the results of the X-ray diffraction for the plasma sprayedcoatings are shown in Fig. 5 (b). It shows that the main phases present are TiC



a) Powder : phases detected were TiC and Ni.

_ti_ H_ ~"- - —- ~

f ^ ^ ^ y ^ s ^ i : ^ ^ ^ ^

b) APS coating : phases detected were TiC and Ni

Fig. 5 Principal phases in (a) TiC-15% Ni powder, and (b) in TiC - 15% Nicoating, as determined by X-ray diffraction method.



and Ni phases. Coatings analysis did not show phase transformation during thethermal spray process.

4 Conclusions

TiC-15% Ni and WC-12% Co coatings were deposited onto mild steel substratesby atmospheric plasma spraying - APS.

TiC-15% Ni coatings had a structure of high porosity, lower values ofhardness and coefficient of friction when compared to the corresponding valuesof WC- Co. The X-ray diffraction (XRD) patterns of the starting powder and theplasma sprayed TiC-15% Ni coating consisted only of TiC and Ni phases. Theresults of volume loss for TiC-15% Ni coatings deposited by atmospheric plasmaspraying were higher than the WC-12% Co sprayed coatings. TiC reinforcedmetal powder coating studied here promise to provide lower coefficient of frictionand better wear performance in coatings of lower porosity, but this must beconfirmed by futher work. Certain applications may benefit from these attributes.

Acknowledgments

The work described in this paper was supported by Commission of the EuropeanCommunities. The authors would like to thank also the London & ScandinavianMetallurgical Co Limited for supplying the powders; the Professor Daniel Biazollifrom Federal University of Umberlandia for providing wearing test equipment,Mrs. Launora Franca for X-ray diffractograms, Mr. Elias Candido and AdelsonProfeta for the mellographic preparation.

5 References

1. Arnell, R.D., Davies, P.B., Hailing, J., Whorney, T.L., Tribology Principlesand Design Applications, McMillan, London, 1991

2. Lugscheider, E., in NTS/87, pp. 105-122, Proceedings of the National Sprayf, Orlando-FL, USA, ASM Int., 1987.

3. Hutchings, I.M., Tribology: Friction and Wear Engineering Materials, pp135-141, Edward Arnold, London, 992.

4. Ericsson, T., Acfa MgfaZ/wrg);, 1966, 14, 858.

5. Holleck, H., Swr/hcz EMg/Mffnfzg, pp 137-144, Vol.7, No. 2, 1991.

6. Schroter, K., German fafenf No 420689 (1923).

7. Atamert, S., Stekly, J., Surfacing Engineering, 1993, Vol. 9, No. 3, pp 231-240.

8. Smith, R. W., Mutasim, Z., Lugscheider, E., Limbach. R., Jungklaus, H.,Ross, J., Cells, J.P., de Bonte, M., Economous, S., in NTS/91, pp 59-66,



Proceedings of the International Thermal Spray Conference, Orlando-FL,USA, ASM Int., 1992.

9. Mutasim, Z., Smith, R.W., Mohanty, M., in NTS/92, pp 1019-1028,Proceedings of the International Thermal Spray Conference, Orlando-FL,USA, ASM Int., 1992.

10. Lugscheider, E., Jungklaus, H., Limbach, R., Smith, R.W., in NTS/92, pp679- 684, Proceedings of the International TJiermal Spray Conference,Orlando- FL,USA, ASM Int., 1992.

11. Vityaz, P., Verstak, A., Sobolevsky, S., Lugscheider, E., Jokiel, P.,Pursche, Chemintz, G., Yushchenko, K., pp 36-40, in Proceeding of theInternational DVS - Thermal Spray Conference, Aachen, Germany, ASM Int.,1993.

12. Smith, R.W., Gentner, D., Harzenski, E., Robisch, T., pp 299-306, inNTS/88, Proceedings National Thermal Spray Conference, Cincinnati,Ohio, USA, SM Int., 1988.


382 Surface Treatment, Computer Methods and ......Wear behaviour of plasma sprayed TiC-15%Ni...

Documents

Transcript of 382 Surface Treatment, Computer Methods and ......Wear behaviour of plasma sprayed TiC-15%Ni...