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Surface & Coatings Technology 194 (2005) 10–15

High temperature tribology behaviors of brush plated

Ni–W–Co/SiC composite coating

Xu Jianga,*, Wenjin Liua, ShiYun Dongb, BinShi Xub

aLaser Processing Research Center, Mechanical Engineering Department, Tsinghua University, Beijing 10084, PR ChinabArmored Force Engineering Institute, Beijing 100072, PR China

Received 15 November 2003; accepted in revised form 30 April 2004

Available online

Abstract

The high temperature wear behavior of Ni–W–Co/SiC composite brush plated coatings deposited on a hot work die steel has been

investigated using a plate-on-ring test rig. The microstructure and wear characteristics of coating have been analyzed by scanning

electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that typical

microstructure of Ni–W–Co/SiC composite coating consists of Ni-based solid solution and SiC particles. The TEM observation of Ni–

W–Co/SiC composite coating has revealed the fine SiC particles of nano-size in the brush plated coatings and the matrix of Ni–W–Co

plated coating is composed of a mixed crystalline and amorphous structure. The worn surface morphology of the plated coating is

observed by SEM and laser profile analysis. In the temperature range 400–600 jC, wear rate and average friction coefficient of the Ni–

W–Co/SiC brush plated composite coatings are lower than that of the 3Cr2W8V (ASTM H21) hot work die steel. Abrasive and

adhesive wears are the major wear mechanisms of brush plated composite coating at high temperature.

D 2004 Published by Elsevier B.V.

Keywords: Ni–W–Co/SiC composite coating; Brush plated; Wear resistance

1. Introduction

Failure due to high temperature wear is a major problem

in hot forging processing. About 70–80% of die in hot fail

by wear damage. The life of dies has been prolonged and

cost reduced by increasing wear resistance of material used

in high temperature environments. 3Cr2W8V steel (ASTM

H21) hot work die, which has good mechanical properties, is

widely used as hot forging dies material in China. Owing to

low thermal stability, 3Cr2W8V (ASTM H21) hot work die

steel showed brittle fracture, thermal fatigue and low wear

resistance.

The application of surface treatments on materials,

such as plated, is an effective way for improving the

tribological behavior of rubbing pairs. The brush plated is

a special electroplated process that is similar to a painting

operation. The equipment is compact and easy to operate.

It is used to coat metal and alloy coatings on surface of

0257-8972/$ - see front matter D 2004 Published by Elsevier B.V.

doi:10.1016/j.surfcoat.2004.04.095

* Corresponding author.

E-mail address: xujiang73@sina.com.cn (X. Jiang).

varying size and shape. This technology is initially

applied to surface decorating and mechanical repairing.

In recent years, with the development of electric brush

plated technology, high attention has been given to the

research aspect of surface strengthening of brush plated.

Hui et al. [1–3] showed that corrosion resistance of brush

plated alloy Ni–Fe–W–S coating is superior to that of

electrodeposited chromium and a better wear resistance

than that of electrodeposited chromium at high speed and

heavy load under normal conditions where lubricant was

applied between the contact surface. Ma et al. [4–6]

characterized the friction and wear behaviours of Ni–P

coating using ball-on-disc type apparatus. This work

indicated that Ni–P coating revealed very good properties

of anti-scuffing, anti-wear and reducing friction. In order

to further improve the wear resistance of brush plated

coating, brush plated composite coating which added hard

particle into the plated solution, such as ZrO2, Al2O3, has

been a novel method. Wear resistance of brush plated

Co–Cr2O3 composite coating has possessed a higher wear

resistance than that of hot work die steel [7]. However,

up to now, the research on the wear mechanism of the

Table 1

Chemical composition of experimental material (wt.%)

Specimen C Cr V W Si Mn Fe

3Cr2W8V 0.35 2.42 0.32 8.23 0.20 0.25 bal

Plate material 0.95 1.5 – 0.15 0.2 bal

X. Jiang et al. / Surface & Coatings Technology 194 (2005) 10–15 11

brush plated composite coating is still at primary stage.

This paper is aimed at investigating the wear character-

istic and mechanism of Ni–W–Co/SiC composite coating

in the temperature range 400–600 jC.

2. Experimental method

3Cr2W8V (ASTM H21) hot work die steel (chemical

composition listed in Table 1) was used as substrate

materials. The steel was heat-treated by austenitizing at

1180 jC, quenching in salt bath, followed by tempering

3 h at 560 jC, with a hardness of HV660. The plated

tool is soaked in the plated solution and then the plated

substrate material was deposited by brush plated tool

against the substrate material. Plated solution was deliv-

ered to the work area by a porous, absorbent cover

wrapped over the anode of the plated tool. The compo-

sition of electric brush Ni–W–Co/SiC solution was:

H2SO4�7H2O, 380–450 g/l Na2WO4�7H2O, 20–30 g/l

HCOOH, 30–40 g/l H3C6H5OH2O, 20–30 g/l

H3BO3, 30–35 g/l CH3COOH, 18–25 g/l

Na2SO4, 6–8 g/l NaF, 4–6 g/l

CoSO4�7H2O, 2–3 g/l MnSO4�H2O, 2 g/l

MgCl2�12H2O, 2–3 g/l Cl12H25NaSO4, 0.01 g/l

SiC, 6–8 g/l

Fig. 1. The OM morphology of the brush plated Ni–W–Co/SiC composite

layer.

For this series of experiments, the value of pH of the plated

bath was 1.4–2.0 and size of SiC particle was 40–100 nm.

Electric brush plated was operated at a working voltage of

12–14 Vand relative velocity between the positive electrode

(plated tool) and negative electrode (substrate materials) was

11 m/min. The Ni–W–Co/SiC plated coating with a deposit

thickness of 50 Am was obtained.

The chemical compositions and microstructure of the

surface coating were analyzed by JSM-35C scanning

electron microscopy (SEM) and X-ray energy dispersive

spectroscopy (X-EDS). The phase structure identification

was determined using D/Max-RB X-ray diffraction

(XRD) studies using Cu-Ka radiation. A Hitachi H-800

TEM was used to identify the phase.

High temperature wear tests were fulfilled on a plate-on-

ring apparatus (type MG-200) with coated specimen serving

as the ring under dry condition with temperature from 400 to

600 jC. The apparatus(typeMG-200) has been described in a

previous publication [8]. The test rig consisted of loading

lever, specimen hold, drive motor, heating furnace, temper-

ature monitored system and measuring equipment. During

the experiments, friction force was recorded on line via

torque as measured by the strain gauge mounted in the

vertical arm. The ring specimen with a diameter of 66 mm

was mounted on the upper holder. The plate specimen with a

diameter of 70mmwas fixed to the rotating lower holder. The

plate specimen was fabricated from a high carbon quenched-

and-tempered steel (chemical composition listed in Table 1)

with a Rockwell C hardness of 61HRC. All the tests were

conducted without lubrication and the applied normal load

varied from 49 to 98 N.

A conventional scratch tester (WS-97 equipped with an

acoustic emission detector) was used to evaluate the

adhesion of coating to substrate. The radius of the

diamond pin was 0.2 mm. All the tests were performed

employing a continuous increase in the normal load, from

0 to 100 N, at a loading rate of 100 N min� 1. Surface

hardness of coatings was determined with Vickers pyra-

mid-indentation method using a 1 N load.

3. Results and discussion

3.1. Microstructure of brush plated Ni–W–Co/SiC com-

posite coating

The typical OM micrograph of Ni–W–Co/SiC com-

posite coating are shown in Fig. 1. From the micrograph,

the fine grain of Ni–W–Co/SiC composite coating is

observed. The transmission electron microscopy (TEM)

micrograph (Fig. 2) of Ni–W–Co/SiC composite coating

has revealed the fine SiC particle of nano-size in the

brush plated coating and matrix of Ni–W–Co plated

coating is composed of crystalline and amorphous struc-

ture. It confirms that A district possesses crystalline

character and amorphous character is obviously observed

at B district by TEM diffraction of brush plated Ni–W–

Co/SiC composite coating.

Fig. 3 presents a typical X-ray diffraction spectra

obtained from Ni–W–Co/SiC composite coating. It

shows that typical microstructure of Ni–W–Co/SiC

composite coating consists of Ni-based solid solution.

Fig. 2. The TEM morphology of the brush plated Ni–W–Co/SiC composite layer and diffraction pattern.

X. Jiang et al. / Surface & Coatings Technology 194 (2005) 10–1512

The added SiC particle into the plated solution is only

6–8 g/l, thereby the volume fraction of the added SiC

particle in the plated coating is less than 10% and the

peak of SiC has not been found by the X-ray diffraction

spectra.

3.2. Adhesion strength and hardness of Ni–W–Co/SiC

composite coating

Fig. 4 presents the result of adhesion strength of coating

to substrate by scratch test. From this figure, the critical load

of Ni–W–Co/SiC composite coating is 70 N, which is

characterized by having a strong adhesive force with the

Fig. 3. The ZRD spectra of the brush plated Ni–W–Co/SiC composite

layer.

substrate (a carbon steel substrate). The microhardness of

Ni–W–Co/SiC composite coating is HV990. Because of a

little of codeposition of hard particle in composite coating,

the hardness of Ni–W–Co/SiC composite coating is obvi-

ously higher than that of 3Cr2W8V (ASTM H21) hot work

die steel.

3.3. Wear rate and coefficient of friction in high

temperature

Fig. 5 shows variation of wear rate and average friction

coefficient value for Ni–W–Co/SiC composite coating

and 3Cr2W8V (ASTM H21) hot work die steel at various

temperatures with sliding distance at applied load of 74 N

at a sliding speed of 1 m s� 1. The wear rate of Ni–W–

Co/SiC composite coating and 3Cr2W8V (ASTM H21)

hot work die steel decrease with increasing test tempera-

ture to a critical temperature (500 jC) and subsequently

increase with further increasing temperature. The friction

coefficient of Ni–W–Co/SiC composite coating and

3Cr2W8V (ASTM H21) hot work die steel first decrease

with temperature but then increase with further increasing

temperature. At 500 jC, the Ni–W–Co/SiC composite

coating and 3Cr2W8V (ASTM H21) hot work die steel

exhibit the lowest wear rate and friction coefficient. The

Ni–W–Co/SiC composite coating reveals the low wear

rate and friction coefficient compared with that of the

3Cr2W8V (ASTM H21) hot work die steel, which repre-

sents that wear resistance of the Ni–W–Co/SiC compos-

ite coating is superior to that of 3Cr2W8V (ASTM H21)

hot work die steel at tests temperature. Fig. 6 show the

Fig. 4. The result of adhesion strength of Ni–W–Co/SiC composite coatings to substrate.

Fig. 5. The influence of temperature on wear rate and friction coefficient of Ni–W–Co/SiC composite coatings and 3Cr2W8V steel at applied load of 74 N and

sliding speed of 1 m�s� 1. (a) Wear rate, (b) friction coefficient.

Fig. 6. The variation of worn surface roughness of Ni–W–Co/SiC

composite coatings and 3Cr2W8V steel after test with various temperatures

at applied load of 74 N and sliding speed of 1 m�s� 1.

X. Jiang et al. / Surface & Coatings Technology 194 (2005) 10–15 13

variation of worn surface roughness of Ni–W–Co/SiC

composite coating and 3Cr2W8V (ASTM H21) hot work

die steel after test at various temperatures at applied load

of 74 N and sliding speed of 1 m�s� 1. The results show

similar trends to that of wear rate and friction coefficient.

As shown in Fig. 6, the worn surface roughness of Ni–

W–Co/SiC composite coating is smaller than that of

3Cr2W8V steel, which represents that intensity of friction

of Ni–W–Co/SiC composite coating is lower than that of

3Cr2W8V steel.

3.4. Effect of applied load on wear rate

The variation of wear rates of Ni–W–Co/SiC compos-

ite coating and 3Cr2W8V (ASTM H21) hot work die steel

with applied load at sliding speed of 1 m�s� 1 and

temperature at 500 jC is shown in Fig. 7. As the applied

load is raised from 49 to 98 N, the wear rates of Ni–W–

Co/SiC composite coating and 3Cr2W8V (ASTM H21)

Fig. 7. The variation of wear rates of Ni–W–Co/SiC composite coatings and

3Cr2W8V steel with applied load at sliding speed of 1 m�s� 1 at 500 jC.

X. Jiang et al. / Surface & Coatings Technology 194 (2005) 10–1514

hot work die steel are increased correspondingly. In

contrast, the increase in wear rate for 3Cr2W8V (ASTM

H21) hot work die steel is larger than that for the Ni–W–

Co/SiC composite coating. With the hard particle of SiC,

the Ni–W–Co/SiC composite coating has higher surface

hardness, and ability to resist plastic deformation is

enhanced.

3.5. Worn morphology and wear mechanisms

Fig. 8 shows the morphology of worn surface of the Ni–

W–Co/SiC composite coating after tests at applied load of 74

Fig. 8. SEMmicrograph of worn surface of Ni–W–Co/SiC composite coating afte

(c) 600 jC.

N at various temperatures. At 400 jC, the worn surface

exhibits some ploughed grooves in Fig. 8(a). It is inferred

that abrasive wear was the predominant mechanism. With

hard particle reinforced brush plated coating, the Ni–W–Co/

SiC composite coating can be good for resisting against

penetrating and cutting action during dry sliding. It may be

seen that the wear surface is relatively smooth and has few

scratch regions at 500 jC in Fig. 8(b). The reason is that self-

lubricating NiO film formed on the worn surface of brush

plated coating which can obviously improve the tribological

properties of brush plated coating. The SEM micrograph of

worn surface of the brush plated coating tested at 600 jC is

presented in Fig. 8(c). From Fig. 8(c), the worn surface is

much rougher and exhibits severe adhesion and peeling. It

indicates that the adhesive wear is predominantly wear

mechanism. This reason is relative to the hardness of Ni–

W–Co/SiC composite coating reduced swiftly, which does

not sustain the protective oxide film.

4. Conclusion

The wear resistance of the Ni–W–Co/SiC composite

coating is higher than that of 3Cr2W8V (ASTM H21) hot

work die steel at test temperature. At 500 jC, the Ni–W–

Co/SiC composite coating exhibits the lowest wear and

coefficient of friction in the test temperature range 400 to

600 jC. With the normal load increasing, the wear rate of

Ni–W–Co/SiC composite coating and 3Cr2W8V steel

increase correspondingly.

r tests at applied load of 74 N at various temperature: (a) 400 jC, (b) 500 jC,

X. Jiang et al. / Surface & Coatings Technology 194 (2005) 10–15 15

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