Sliding wear behavior of niobium carbide coated AISI 1040 steel

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Wear 264 (2008) 219–225

Sliding wear behavior of niobium carbide coated AISI 1040 steel

Saduman Sen, Ugur Sen ∗Sakarya University, Technical Education Faculty, Department of Metal Education, 54187 Esentepe Campus, Sakarya, Turkey

Received 18 October 2006; received in revised form 27 January 2007; accepted 9 March 2007Available online 15 May 2007

bstract

In the present study, the wear and friction behavior of AISI 52100 steel and alumina against niobium carbide coated AISI 1040 steel disk wastudied using ball-on-disk arrangement. Niobium carbide coating treatment was performed on AISI 1040 steels using thermo-reactive diffusionechniques. The presence of NbC phase in the coating layer was confirmed by X-ray diffraction analysis. Friction and wear tests were carriedut at dry test conditions under 2.5, 5 and 10 N loads at 0.1 m/s sliding speed. The results showed that the friction coefficient values are 0.4–0.68or AISI 52100 steel and 0.4–0.55 for alumina ball, respectively. The specific wear rate of AISI 52100 steel is ranging between 5.66 × 10−6

nd 3.79 × 10−5 mm3/N m. For alumina, it ranges between 3.03 × 10−8 and 6.36 × 10−7 mm3/N m. In case of alumina running against niobiumarbide coated disk, the wear rate obtained from wear tracks on the disk is ranging between 1.44 × 10−6 and 7.55 × 10−6 mm3/N m. In general, theoefficient of friction and wear rate increased with the increase in load value.

2007 Elsevier B.V. All rights reserved.

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eywords: Niobium carbide coating; Friction; Wear; AISI 1040 steel

. Introduction

Hard coating with a nitride, carbide or carbonitride is aommon method for improving the wear resistance of ferrousaterials. This can be achieved by vapor deposition process,

uch as physical vapor deposition (PVD) and chemical vaporeposition (CVD) [1]. An alternative method is the thermo-eactive diffusion (TRD) technique which can be applied forbtaining niobium carbide coating on iron based alloys [2–6].here are many reports in literature, related to niobium carbideoating and its properties [7–12]. The use of hard coatings to pro-uce wear resistant surface layers that can increase tool life orfficiency is now well accepted [13–15]. Niobium carbide (NbC)resents a number of potentially interesting characteristics forts use in wear applications, such as high hardness [16], highoughness, extremely high Young’s modulus and high meltingemperature (3873 ◦C) [17].

The wear and friction properties of niobium carbide coated

teel have yet been studied extensively. Arai et al. studied prac-ical use of NbC coated steels in industrial application, such asurface finishing, sand crushing, metal cutting application, etc.

∗ Corresponding author. Fax: +90 264 346 02 62.E-mail address: [email protected] (U. Sen).

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043-1648/$ – see front matter © 2007 Elsevier B.V. All rights reserved.oi:10.1016/j.wear.2007.03.006

ear resistance of NbC coated steels by TRD method is excel-ent. Previous studies showed that NbC coating was of higherear resistance than that of borided, hardened and nitrided steel,eing nearly equal to that of VC, TiN, TiC and TiCN coated steels18,19].

The aims of this study are to produce niobium carbide thinayer on the steel substrate by TRD method and to investigatehe friction and wear characteristics of alumina and AISI 52100gainst niobium carbide coated steel disk. Wear test was carriedut with ball-on-disk arrangement at 2.5, 5 and 10 N load and.1 m/s sliding speed.

. Experimental procedure

.1. Sample preparation

Niobium carbide coating was performed on pre-normalizedISI 1040 steel with initial hardness value of 145 HV and con-

isting of 0.41% C, 0.2% Si, 0.74% Mn, 0.024% P, 0.032%, 0.0287% Cr, 0.019% Mo, 0.021% Ni and 0.001% V.oating treatment was realized by pack method in an envi-

onment containing of ferro-niobium, ammonium chloride andlumina.

The structural characterization of the niobium carbide layeras examined using B O71 Olympus optical microscope, JEOL

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220 S. Sen, U. Sen / Wear 264 (2008) 219–225

Table 1Niobium carbide coating process conditions and properties of the coated steel

Parameters Properties

Coating temperature (◦C) 1000Treatment time (h) 2Coating bath mixture Ferro-niobium, NH4Cl, Al2O3

Coating method Thermo-reactive deposition techniqueCoating sample AISI 1040Dimensions of samples 20 mm in diameter, 5 mm in heightCoating layer thickness (�m) 13Coating hardness (HK0.01) 2512 ± 190Coating layer roughness, Ra (�m) 0.11

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TW

P

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asFloads of 10 g. The surface roughness of the coating layers wasalso measured using a Perthern profilometer and the value isRa = 0.11 �m. The process conditions are presented in Table 1.

Fig. 1. Schematic illustration of ball-on-disk wear test [20].

SM-5410 scanning electron microscope and XRD analysis.RD analysis was performed on the sample surface using Cu

� radiation with a wave length of 1.5405 A, over a 2θ range of0–110◦ with of 0.070◦ increments per second. The thicknessf niobium carbide layer was measured by an optical microm-ter attached to the optical microscope. The layer thickness is

able 2ear and friction test parameters

arameters Selected value

pplied load (N) 2.5, 5 and 10elocity (m/s) 0.1otating speed of the disk (rpm) 190ear track diameter (mm) 10

emperature (◦C) 21 ± 3umidity (%) 65 ± 5uration (min) 60est balls Alumina, AISI 52100 steel

ig. 2. (a) Optical and (b) SEM micrographs of niobium carbide coated AISI040 steel.

bout 11 �m. The hardness of niobium carbide layer and sub-trates were measured on the cross-sections using a Future-TechM-700 micro-hardness tester with Knoop indenter under the

Fig. 3. XRD pattern of niobium carbide coated AISI 1040 steel disk.

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S. Sen, U. Sen / Wear 264 (2008) 219–225 221

Fig. 4. The coefficient of friction of alumina ball against the niobium carbidecoated AISI 1040 steel disk.

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Fig. 6. Optical micrographs of wear scar of alumina ball worn against niobium ca

ig. 5. The coefficient of friction of hardened AISI 52100 steel ball against theiobium carbide coated AISI 1040 steel disk.

rbide coated steel disk and wear track of niobium carbide coated steel disk.

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wball diameter, S the sliding distance and P is the applied load.

22 S. Sen, U. Sen / We

.2. Wear test

Ball-on-disk arrangement was used for friction and wear testsee Fig. 1). The alumina and steel balls, 9.5 mm in diameter,ere used in the wear test. Alumina ball has mirror like surfacenish with a hardness value of 2250 VHN. AISI 52100 steelall has 0.003 CLA roughness with a hardness value of 780HN. Most of the materials are encountered with ambient tem-erature and humidity in the industrial applications. Therefore,he friction and wear tests were carried out at room temper-ture (21 ± 3 ◦C), relative humidity being 65 ± 5 conditions.he load conditions were chosen to cover the practice condi-

ions (in industry) under which these materials are used. Beforeach test, the ball and disk were ultrasonically cleaned in ace-one and ethyl alcohol for 10 min and then rinsed in acetone.

ear tests were carried out under 2.5, 5 and 10 N load val-es and at 0.1 m/s sliding speed (see Table 2). Mean Hertzianontact pressures calculated for alumina and AISI 52100 steelnder the loads of 2.5, 5 and 10 N are 389, 491, 618 and 319,02, 506 N/mm2, respectively. Knowing that, the compressive

ield strength of AISI 52100 steel and alumina are 2584 and600 MPa, respectively. Multiple tests (up to three repeats) forhe same test conditions showed that the wear rate data were veryroducible, with standard deviations being less than 13.6% of

eia

Fig. 7. SEM micrograph and X-ray maps (a), EDS analy

4 (2008) 219–225

he mean value (within a 95% confidence level) and the averagealue reported.

The wear volumes were measured from ball scar and diskalue. The volume from wear track was measured using cross-ection area of wear track (A), which was determined using aurface profilometer. In the measurements, the standard devia-ion on the worn track was typically less than 10% of its averagealue. The wear volume, Vd, is calculated using [21]:

d = 2πrA (1)

here r is the radius of the wear track. The wear volume fromall scar was measured using optical micrometer attached to theptical microscope. The specific wear rate of the ball (Vb) wasalculated using [22];

b = πd4

64DSP(2)

here d is the wear scar diameter of the worn area of ball, D the

Finally, the structure and topography of ball surfaces werexamined by optical microscope, while wear track was exam-ned using optical microscopy, scanning electron microscopynd energy dispersive X-ray spectroscopy (EDS).

sis of wear track (b) and niobium carbide layer (c).

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S. Sen, U. Sen / We

. Result and discussion

Optical and SEM cross-sectional examinations of niobiumarbide coated AISI 1040 steel revealed that the niobium car-ide layer formed on the substrate is dense, compact and firmlyonding to the steel substrates (ferrite + pearlite microstructure)see Fig. 2). Furthermore, the XRD analysis of niobium car-ide coating layer shows the presence of NbC phase (non-oxidearbide type ceramic) and is indicated with character ‘1’ (seeig. 3). This result is in agreement with Refs. [4,21,22]. Theardness of NbC coating layer and matrix are 2512 ± 190 and29 HK0.01, respectively.

Figs. 4 and 5 present the variation of coefficients of frictionersus sliding distance for the alumina and hardened AISI 52100teel against niobium carbide coated AISI 1040 steel disk. It islear from Figs. 4 and 5 that the coefficient of friction of testedaterials increase with sliding distance up to 100 m, approxi-ately. Over this distance, there is no any significant change

n coefficient of friction values. The coefficient of friction oflumina under 2.5, 5 and 10 N loads are 0.4, 0.49 and 0.51,espectively. It is also clear from these figures that the higher

ist

ig. 8. Optical micrographs of wear scar of hardened AISI 52100 steel ball worn agaiteel disk.

4 (2008) 219–225 223

he load, the higher is the coefficient of friction value. A 100nd 300% increase in load value resulted in 22.5 and 27.5%ncrease in coefficient of friction. In case of AISI 52100 steel,he value coefficient of friction are 0.34, 0.47 and 0.68 under 2.5,and 10 N load values, respectively. A 100 and 300% increase

n load values resulted in 38.2 and 100% increase in coefficientf friction. This could be explained by the increase in tempera-ure on the worn track of the NbC coated disk due to increase inoad value and caused the more oxidation. Figs. 6 and 7 presentptical micrographs, SEM images, X-ray maps and EDS analy-is for alumina worn surfaces. It is clear from Fig. 6 that theigher the load, the wider and the darker is the wear track.urthermore, Fig. 7 shows the oxygen content increase on theear track. This figure also shows that wear behavior of nio-ium carbide coated steel disk worn against alumina is abrasivend oxidative. Figs. 8 and 9 present optical micrographs, SEMicrographs, X-ray maps and EDS analysis for AISI 52100

teel worn surfaces. It is clear from Fig. 8 that the increase

n load value caused an increase in the smeared area on theteel track. Furthermore, Fig. 9 shows that smeared zones onhe worn track of the disk include iron and oxygen. This indi-

nst niobium carbide coated steel disk and wear track of niobium carbide coated

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224 S. Sen, U. Sen / Wear 264 (2008) 219–225

teel is

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iaand 5.66 × 10−6–3.79 × 10−5 mm3/N m, respectively. The spe-cific wear rate for niobium carbide coated disk ranges between1.44 × 10−6 and 7.55 × 10−6 mm3/N m.

Fig. 9. SEM micrograph and X-ray maps (a), EDS analysis of smeared s

ates that, smeared steel was oxidized during wear process. It iselieved that, the increase in coefficient of friction of the steelesulted from the formation of more iron oxide on the wearrack with increase in load. Furthermore, this smeared surfacen Figs. 8 and 9 is evident that the wear mechanism is adhesivend oxidative.

Fig. 10 presents the variation of specific wear rate for alu-ina, AISI 52100 steel and niobium carbide coated disk with

oad value. It is clear from this figure that the specific wear ratencreases with the increase in load. In addition, the wear ratef alumina is much lower than that of AISI 52100 steel. Thisould be due to the higher hardness of the alumina, because thencrease in wear rate is inversely proportional to the decreasen hardness values of the materials [23]. Furthermore, Rigneyxplained that the effect of hardness on the sliding behavior isuch more varied and complex [24]. In case of wear loss mea-

ured from the wear scar on the alumina ball and AISI 52100teel, there is an increase of 18 and 72% in the specific wearate for an 100% increase in the applied load, respectively.n the other hand, for 300% increase in load, these values

re 2000 and 570%, respectively. In case of the alumina ballgainst niobium carbide coated steel disk, the wear rate was cal-ulated from worn volume of wear track. The results showedhat, there is a 424% increase in wear rate for a 300% increase

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land (b) and niobium carbide layer took place between steel islands (c).

n load value. Finally, the volumetric wear rates of aluminand AISI 52100 steel range between 3.03 × 10−8–6.36 × 10−7

ig. 10. Specific wear rate of alumina, hardened AISI 52100 steel ball andiobium carbide coated steel disk against alumina ball.

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S. Sen, U. Sen / We

. Conclusions

The results of this work demonstrate that well adhereddiffusion controlled) niobium carbide coating can have veryeneficial effect on the tribological behavior of thermo-hemically treated and coated steel surfaces. It is concludedhat:

1) Niobium carbide coating can successfully be deposited onthe AISI 1040 steel by pack method.

2) Niobium carbide layers coated on the steel substrate arecompact, smooth, porosity-free and homogeneous.

3) The hardness of niobium carbide layer coated on AISI 1040steel is 2512 ± 190 HK0.01.

4) The phase formed in the coating layer is NbC.5) The coefficients of friction for all combinations increase

with the increase in load.6) The coefficient of friction of alumina against niobium car-

bide coated AISI 1040 steel ranges between 0.4 and 0.55and that of AISI 52100 steel against niobium carbide coatedsteel disk ranges between 0.38 and 0.67.

7) For all materials, wear rate increased with increasing load.8) Higher wear rate was observed in hardened AISI 52100 steel

ball worn against niobium carbide coated AISI 1040 steeldisk under the load of 10 N.

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