Wear resistance of thermal sprayed coatings on the base of recycled hardmetal.pdf

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.Surface and Coatings Technology 130 2000 4651

Wear resistance of thermal sprayed coatings on the base ofrecycled hardmetal

Priit Kulu, Sergei Zimakov

Department of Materials Technology, Tallinn Technical Uniersity, Ehitajate tee 5, 19086 Tallinn, Estonia

Abstract

.The application of used recycled hardmetal base powders for new composite powder production for thermal spraying wasstudied. The detonation method for the deposition of sprayed WC-Co hardmetal coatings and spray and fusion technology forlaying of melted self-fluxing alloybase composite coatings containing WC-Co hardmetal particles were used. The abrasion-erosion wear resistance of sprayed WC-Co hardmetal coatings and composite coatings from self-fluxing Ni-base alloy and WC-Cohardmetal powders was evaluated. The prospects of used hardmetal base powder application for thermal spraying were shown.The wear resistance of sprayed used WC-Co hardmetal-based coatings was two times lower than comparative coatings from

Amdry powder; the spray and fused composite coatings exhibited a 200% higher wear resistance than non-coated steel. The waysof improving the abrasion-erosion wear resistance of sprayed and melted used WC-Co hardmetal powder-based thermal sprayedcoatings are offered: using a narrow range of granulometry of powder, plated with Co and Ni hardmetal powder and powder withspheroidal particles. 2000 Elsevier Science S.A. All rights reserved.

Keywords: Thermal spray coating; Wear; Abrasion-erosion; Hardmetal; Recycling

1. Introduction

In terms of product lifetime for engineering materi-als and parts, the surface is of prime concern. Thisinvolves both corrosion behavior and mechanicalproperties such as material wear. To protect against

corrosion and increase the wear resistance of materialsand parts, various coating techniques have provedeffective. For strengthening parts subjected to the in-tensive abrasion-erosion wear at extreme conditions .high velocities and pressure, cyclic impact load, etc.gas thermal coatings are highly effective. Recent atten-tion has focused on reduced consumptions of existingresources and materials recycling. Therefore, the appli-

.cation of composite powders based on used recycledhardmetals for thermal spraying is topical.

Corresponding author. Tel.: 372-620-3352; fax: 372-620-3196. .E-mail address: [email protected] P. Kulu .

This paper discusses the abrasion-erosion wear resis-tance of gas thermal coatings deposited by detonationspraying and gas flame spray and fusion onto 0.45% Csteel substrates.

2. Experimental details

2.1. Coating materials

We used WC-Co hardmetal powders, produced fromrecycled hardmetal by disintegrator milling, as basic

components of detonation sprayed coatings 1,2 . Parti- .cle size ranged from 32 to 160 m Table 1 . Fig. 1a

illustrates the particle shape from 125 m. Particleswere primarily equiaxed in form, and their microstruc-ture showed a typical hardmetal structure based ontungsten carbide.

For comparison, we used the hardmetal powder WC-12Co, specified as Amdry 927 from 10 to 45m Sulzer

0257-897200$ - see front matter 2000 Elsevier Science S.A. All rights reserved. .PII: S 0 2 5 7 - 8 9 7 2 0 0 0 0 6 8 7 - 3


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( )P. Kulu, S. Zimako Surface and Coatings Technology 130 2000 4651 47

.Metco Inc. and aglomerated and sintered WC-15Co,specified as Kiev BK15B from 40 m Institute of

.Welding, Kiev, Ukraine . Fig. 1b,c illustrates the parti-cle shape of these powders.

The spray and fused coatings contained NiCrSiB

alloy powders as basic components. Table 2 shows thechemical composition of the self-fluxing alloy powdersfor the powder composites. With a spherical shaped,their particle size was 60100 m.

We studied the effect of matrix hardness, hard phasecontent and hardmetal particle size on the abrasion-erosion wear resistance.

We used different methods sieving, image and laser.analysis for granulometry and morphology description

of the powders produced by mechanical milling fromrecycled hardmetal.

2.2. Coating technology

Sprayed coatings were deposited by the detonationmethod on structural steel of 0.45% C content as thesubstrate material. The hardness of the substrate mate-rial was 200 HV. Spray parameters are shown in Table3. Hardmetal powders of size ranging from 32 to 160m were sprayed by means of the Perun-S Detonation

.Spray System Institute of Welding, Kiev, Ukrainewith propane and oxygen as combustion gases.

We studied the influence of hardmetal particle sizeon the efficiency of spraying thickness of layer per

.shot and the properties of the coatings.The spray and fused coatings based on self-fluxing

alloys with WC-Co hardmetal particles from 60 to 500m were deposited by the Eutalloy Flame Gun Casto-

.lin SA, Switzerland on structural steel of 0.45% Ccontent as the substrate material. Acetylene and oxy-gen were used as combustion gases.

The detonation sprayed coatings were approximately0.3 mm thick, and the spray and fused coatings werefrom 0.5 to 1 mm thick.

2.3. Abrasion-erosion wear testing

Modelling of wear and the study of wear mechanism

were performed in a centrifugal accelerator as shown in Fig. 2 3 . Our testing method comprised the abrad-

ing of the specimens with a stream of abrasive quartzsand particles. Table 4 demonstrates the parameters ofwear.

Based on the weight loss of abraded material, wearfactors loss of mass or volume per 1 kg of abrading

material in milligrams per kilogram and millimeters.cubed per kilogram, respectively were calculated. The

relative wear resistance E was calculated as the ratioof the wear rates of the coated and non-coated subs-trate material.

3. Results and discussion

3.1. Structure, porosity and hardness of the coatings

The cross-section of detonation sprayed coatings isshown in Fig. 3. Their porosity depended on the parti-cle size of the used hardmetal powders, ranging from

.4.1 to 16.5% Table 5 . .The cross-section of the NiCrSiB-25 wt.% WC-15Co

coating is shown in Fig. 4. NiCrSiB self-fluxing alloyforms a matrix with WC-Co hard particles, which are

partially dissolved in the Ni-base matrix 4 .The results of the study demonstrated that powder

particle size had a great influence on the thickness ofthe obtained detonation sprayed coatings. As shown inTable 6, with fine powders, thickness per shot was

approximately two times higher. More important is theparticle shape of the spraying powder: with the spheri-

.cal powder WC-12Co Amdry , the coating thicknesswas three to four times higher than that with theisometric powder produced by mechanical milling ofrecycled hardmetal.

3.2. Wear resistance of sprayed coatings

The abrasion-erosion wear resistance of the detona-tion sprayed coating from recycled hardmetal powders

.at small impact angle 30 was not high approxi-mately two times lower than that of comparative coat-

.ings from Amdry powder Table 7 .

Table 1Main characteristics of hardmetal powders

Type of Granulometry Characterization of powders .powder m 2 . . .Main fraction m 70% Surface in wt. unit m g

For detonation spraying 3240 1530 0.0936380 4070 0.088

80 90140 0.085

For composite melted coatings 60125 3060 0.006125250 70230 0.003

250500 270400 0.001


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( )P. Kulu, S. Zimako Surface and Coatings Technology 130 2000 465148

Fig. 1.

Table 2Chemical composition of self-fluxing alloy powders

.Powder Granulometry Chemical composition wt.%a .codes m Ni Cr Si B

12494 60100 Base 8.014.0 1.22.3 1.72.512495 60100 Base 10.016.0 3.05.0 2.04.012496 60100 Base 12.018.0 3.55.5 2.54.5

aPowders of Castolin SA, Switzerland.

The low wear resistance of the sprayed coatings fromrecycled hardmetal powders is caused by the peculiari-ties of the powders produced by mechanical milling ofthe hardmetal. As the reduction of hardmetal part sizeby impact loading takes place by the transcrystalline

failure of the tungsten carbide hard phase the line offracture passes through the tungsten carbide grains,

.and not round their boundaries binder metal , eachhardmetal powder particle is a composite materialouter surface of the particle is WC, binder phase-Co is

. inside the particle . As shown in 5 , the wear resistanceof sprayed coatings from pure hard phase powders ormechanical mixture of powders is lower by one order ofmagnitude than that of coatings from alloy powders.Based on the wear mechanism study, the wear of thecoating results from the direct fracture of carbides and

.low cyclic fatigue of the matrix metal Fig. 5a or from .microcutting Amdry powder Fig. 5b . It differs

from the wear of hardmetals 6 and from the abrasive wear in other conditions 7 .

3.3. Wear resistance of spray and fused coatings

Table 8 shows the relative wear resistance of conven- .tional melted NiCrSiB 12494 coating and that of the

coatings reinforced with hardmetal particles. As shown,the wear resistance of the composite coatings exceedsthat of conventional NiCrSiB coating by a factor ofapproximately 1.5. Depending on the hardmetal parti-cle content, the coating with 1550 wt.% of hardmetalshowed a relative wear resistance of 1.32 times that of

.pure NiCrSiB coating Table 8 .With the difference in the wear resistance of thecoatings from pure self-fluxing Ni-base alloys of dif-

ferent hardness up to two times 4 , the effect of theNiCrSiB matrix hardness on the wear resistance ofcomposite coatings was insignificant; the wear factorsdiffered by only 3040%. This is because the hardnessof the matrix phase is higher than that of a matrixwithout hardmetal particles. The higher hardness isattributed to dissolved hardmetal particles within the

.Fig. 1 Micrographs of hardmetal powders: a WC-15 Co powder . .from125 m; b WC-15Co Kiev powder; and c WC-12Co Amdry

powder.


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( )P. Kulu, S. Zimako Surface and Coatings Technology 130 2000 465150

Table 5Porosity and hardness of detonation sprayed WC-Co hardmetalcoatings

Type of coating Porosity Hardness . .% HV0.2

WC-15Co3240 m 4.1 8156380 m 4.9 76580 m 16.5 780

WC-15Co Kiev BK 15B 2.7 945a

WC-12Co Amdry 927 2.1 6801155

aHardness of Co-based matrixhardness of hardmetal particles.

shown. The lower abrasion-erosion wear resistanceof detonation sprayed hardmetal coatings is due tothe peculiarities of the powders produced by im-pact milling from recycled hardmetal.

2. New NiCrSiB self-fluxing alloybase compositepowders containing WC-Co hardmetal powder .from 15 to 50 wt.% can be produced from used .recycled hardmetals. It was found that the wear

.resistance of melted NiCrSiB WC-Co coatings ishigh. It increased with an increase in the hardphase content in the matrix as well as with anincrease in matrix hardness in the composite at

Fig. 4. Micrograph of the cross-section of spray and fused NiCrSiB-25

.wt.% WC-15Co coating.

Table 6 .Detonation spraying efficiency thickness of layer per shot

.Type of spraying material PorosityThickness m . .and particles size m %Total Per shot

WC-15Co

3240 4050 1.52 4.16380 2535 11.5 4.980 2030 0.71.0 16.5

WC-12Co Amdry 927

1045 150160 55.3 2.1

Fig. 5. Worn surfaces. Topographical images of the sprayed WC-15Co . .coating a and the WC-12Co Amdry coating b at impact angle 30.

small impact angles of abrasive particles. To pre-serve the determined structure of spray and fusedcomposite coatings, methods with long heating andfusion time must be avoided.

3. The wear resistance of thermally-sprayed coatings .can be improved by: a the use of a narrow range

of granulometry of hardmetal powders for detona- .tion spraying; b using hardmetal powder particles

.with plastic metals cobalt or nickel to increase

Table 7Wear resistance of detonation sprayed coatings

Type of coating Wear factor3 .mm kg

WC-15Co3240 m 16.16380 m 17.180 m 18.3

WC-15Co Kiev BK15B 9.4WC-12Co Amdry 927 7.4

Table 8Relative abrasion-erosion wear resistance of spray and fused compos-

.ite NiCrSiB- WC-15Co coatings

Composition of coatings Relative volume wear .resistance E

30 90

NiCrSiB 1.3 0.8NiCrSiB-15 wt.% WC-Co 1.5 0.7NiCrSiB-25 wt.% WC-Co 1.9 0.6

NiCrSiB-50 wt.% WC-Co 2.0 0.6


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( )P. Kulu, S. Zimako Surface and Coatings Technology 130 2000 4651 51

cohesion between particles in the sprayed coatings; .and c the spheroidization of powder particles,

which enhances the technological properties of thespraying powders.

Acknowledgements

This work was supported by the Estonian ScienceFoundation grant No. 3404. Authors would like toacknowledge Dr P. Vuoristo from the Tampere Univer-sity of Technology for performing the detonation spray-ing of coatings.

References

1 A. Tymanok, P. Kulu, D. Goljandin, and S. Roshtsin, in:Proceedings of the 3rd ASM International Conference & Exibi-tion. The Recycling of Metals. BarcelonaSpain, 1997, 513.

2 P. Kulu, A. Tumanok, D. Arensburger, T. Pihl, V. Mikli, H. . .Kaerdi, Proc. Est. Acad. Sci. Eng. 2 1 1996 49.

3 I.R. Kleis, Trans. of Tallinn Polytechnical Institute Ser. A No.. .294 , Tallinn, Estonia, 1970, 23 in Russian .

. .4 P. Kulu, J. Halling, J. Therm. Spray Technol. 7 2 1998 173. . .5 P. Kulu, Tribologia: Finnish J. Tribol. 8 4 1989 12. .6 P. Kallas, J. Wear 198 1996 77. 7 S. Dallaire, J.-G. Legoux, H. Levert, J. Therm. Spray Technol. 4

. .2 1995 163.

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Wear resistance of thermal sprayed coatings on the base of recycled hardmetal.pdf