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Tribological Properties of Laser Surface Texturing and MolybdenizingDuplex-Treated Ni-Base AlloyJIANLIANG LI a; DANGSHENG XIONG a; HONGYAN WU b; ZHONGJIA HUANG a; JIHUI DAI a;RAJNESH TYAGI ac

a Department of Material Science and Engineering, Nanjing University of Science and Technology,Nanjing, China b College of Math and Physics, Nanjing University of Information and Technology,Nanjing, China c Department of Mechanical Engineering, Institute of Technology, Banaras HinduUniversity, Varanasi, India

First published on: 11 January 2010

To cite this Article LI, JIANLIANG, XIONG, DANGSHENG, WU, HONGYAN, HUANG, ZHONGJIA, DAI, JIHUI andTYAGI, RAJNESH(2010) 'Tribological Properties of Laser Surface Texturing and Molybdenizing Duplex-Treated Ni-BaseAlloy', Tribology Transactions, 53: 2, 195 — 202, First published on: 11 January 2010 (iFirst)To link to this Article: DOI: 10.1080/10402000903097478URL: http://dx.doi.org/10.1080/10402000903097478

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Tribology Transactions, 53: 195-202, 2010Copyright C© Society of Tribologists and Lubrication EngineersISSN: 1040-2004 print / 1547-397X onlineDOI: 10.1080/10402000903097478

Tribological Properties of Laser Surface Texturingand Molybdenizing Duplex-Treated Ni-Base Alloy

JIANLIANG LI1, DANGSHENG XIONG1, HONGYAN WU2, ZHONGJIA HUANG1, JIHUI DAI1, and RAJNESH TYAGI1,3

1Department of Material Science and EngineeringNanjing University of Science and Technology, Nanjing, 210094, China

2College of Math and PhysicsNanjing University of Information and Technology, Nanjing, 210044, China

3Department of Mechanical Engineering, Institute of TechnologyBanaras Hindu University, Varanasi 221005, India

Laser surface texturing (LST) and surface molybdenizing

duplex-treatment was performed on Ni-base alloy in order to

improve its wear resistance at high temperature. Surface molyb-

denizing was performed on the laser surface textured Ni-base

alloy by a double glow plasma surface alloying technology.

The friction and wear properties of the duplex-treated, the

single-treated, and the untreated alloys were tested on a ball-

on-disk tribometer by rubbing against an alumina ceramic ball

from room temperature to 600◦C. The topography of the laser

surface textured dimples was measured by a white light interfer-

ometer and optical microscope. The dimples are 150-200 µm

in diameter and 45-50 µm in depth. The distance between the

dimples is 500 µm. The molybdenized layer is approximately

20 µm in thickness. The elastic modulus of Ni-base alloy is im-

proved by molybdenizing. After texturing and the molybdeniz-

ing duplex treatment, the friction coefficient of the Ni-base alloy

decreases from 0.38 to 0.26 at room temperature and from 0.42

to 0.34 at 600◦C. The wear rate of the duplex-treated alloy is

much lower than that of the pristine alloy at 600◦C due to the

textured dimples storing lubricious oxides.

KEY WORDS

Ni-Base Alloy; Double Glow Plasma Surface Alloying; LaserSurface Texturing (LST); Wear Resistance

INTRODUCTION

Adaptive coating with effective lubrication in a varied envi-ronment is a popular subject of study these days. This coating canadopt its lubricant mechanism with the environment, such as inair, vacuum, moisture, or nitrogen atmosphere, even at high tem-perature (Muratore, et al. (1)). The molybdenum can adopt itslubricant mechanism at high temperature through the formationof lubricious oxide (Muratore, et al. (2), (3)).

Manuscript received February 22, 2009Manuscript accepted May 18, 2009

Review led by Thierry Blanchet

Surface texturing, which can improve the elastohydrodynamiceffect under liquid lubrication, is widely studied in the area ofseals (Etsion (4); Schreck and Zum Gahr (5); Etsion, et al. (6);Andersson, et al. (7); Blatter, et al. (8)). When surface tex-tures are used as storage of the solid lubricant, the wear lifeof the lubricating films is prolonged (Basnyat (9); Erdemir, etal. (10)). Voevodin, et al. (11) prepared “chameleon” adaptivecoatings by texturing Ti/TiC/DLC gradient coating and sput-tering deposited MoS2 film. Voevodin and Zabinski (12) stud-ied MoS2/graphite/Sb2O3 as lubricant in textured hard coating.Moshkovith, et al. (13) fabricated micro-dimples by using pulseion energy as the storage sites for MoS2 powder. Adaptive coat-ing is usually obtained by preparation of hard sub-layers withdimples filled with soft solid lubricant, providing easy shear ofthin layers (Rapoport, et al. (14)). Otherwise, texture can be usedas the storage sites of naturally occurring lubricious oxide at hightemperature.

A double glow plasma surface alloying technology, such asmolybdenizing, is an effective method to improve the micro-hardness, wear resistance, and oxidation resistance of metals (Xu,et al. (15); Li, et al. (16)). After molybdenzing on the laser tex-tured surface, the lubricious oxide of molybdenum is helpful forthe wear resistance of the textured surface at high temperature.Meanwhile, the texture can store lubricious oxides and prolongthe life of the oxide film.

In this study, molybdenizing was performed on the tex-tured nickel-base alloy by a double glow plasma alloying tech-nology. The topography, the structure, and the ultra-microhardness of the duplex-treated layer were detected. The fric-tion and wear properties of the untreated, textured, molybd-enized, and duplex-treated layers at elevated temperatures wereinvestigated.

EXPERIMENT

Laser Surface Texturing

The nickel-base alloys with composition of 44.8% Ni,11.2% Cr, 10.0% W, 30% Fe, 3.0% C, and 1.0% Si (wt%) pre-pared by powder metallurgy were mechanically polished untilthey reached a roughness (Ra) below 0.1 µm. The laser surface

195

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196 J. LI ET AL.

Fig. 1—Morphologies of textured surface: (a) optical morphology, lowmagnification; (b) optical morphology, larger magnification; (c)3D profile.

texturing treatment was carried out on the surface of Ni-base al-loy by a ND:YAG pulse laser with a wavelength of 1064 nm, pulseenergy of 30 µJ/pulse, period of 450 ns, and frequency of 100Hz. The dimples were patterned on the surface with a 500 µmseparation. Figure 1 shows the surface morphology and topogra-phy of laser textured surface. The diameters of the dimples are150-200 µm (Fig. 1(a) and 1(b)) and the depths are 40-50 µm(Fig. 1(c)). The roughness (Ra) of the textured surface is about2.3 µm.

Surface Plasma Alloying

Surface molybdenizing was carried out on untextured and tex-tured nickel-base alloys in a multi-function double glow plasma

Fig. 2—SEM morphology of surface of texturing/molybdenizing duplex-treated alloy: (a) low magnification; (b) high magnification.

surface alloying furnace. The double glow plasma alloying deviceconsisted of an insetting anode, cathode, and source pole (target).When the pressure of argon in the vacuum vessel reached a par-ticular value, the glow was ignited by the DC power suppliers.The double glow discharge phenomenon occurred between theanode and the cathode and the anode and the source pole. Thetarget element was sputtered from the source pole and flew tothe surface of the sample (cathode) at a high speed. Meanwhile,the electric energy was transmitted into thermal energy by glowdischarge and the sample was heated to a high temperature. Theions sputtered from the source pole were adsorbed by the work-piece and diffused into the subsurface of the workpiece. Then thealloyed layer, which consisted of the target alloy element, wasformed (Wu, et al. (17)).

The pure molybdenum plate � 100 mm × 5 mm, purity 99.9%,was used as source target, the workpiece of the untextured andtextured nickel-base alloys (� 45 × 7 mm) were used as cath-ode. The distance between the poles was 20 mm. The furnace wasdrawn to a vacuum below 1.0 × 10−2 Pa, then filled with high-purity argon gas until its pressure reached 45 Pa. The voltage ofthe source pole was 900-950 V and the voltage of the cathode

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Tribological Properties of Laser Surface Texturing 197

TABLE 1—CONTENT OF MOLYBDENUM ALONG THE DEPTH OF

MOLYBDENIZED LAYER AS MEASURED BY EDS

Depth (µm) 0 5 10 15 20Mo content (wt%) 34.38 22.01 21.19 17.46 12.72

Fig. 3—SEM morphology of cross section of duplex-treated alloy.

Fig. 4—EDS analysis of element in the dimple.

20 30 40 50 60 70 80 90

1000

2000

3000

I, cp

s

Ni base solutionMo

2θ, °

Fig. 5—XRD pattern of molybdenized alloy.

Fig. 6—Topography of molybdenized texture on nickel-base alloy (a) 2-D;(b) 3-D; (c) cross section profile.

(substrate material) was 400-550 V. The temperature of the sub-strate material, which was measured by an infrared detector, waskept at 950◦C for 4 h.

The morphologies of the duplex-treated alloy were observedby an Olympus optical microscope and SEM attached with en-ergy dispersive spectroscopy (EDS). The topography of the tex-ture was investigated by a white light optical interferometer. Theultra-micro hardness of the molybdenized layer was measuredby DUH-W201/W201S dynamic ultra-micro hardness system(Shimadzu, Japan), which was configured with a Berkovich (3-sided pyramid) diamond tip nano-indenter. The test was con-ducted under the following conditions: Force range: 0.1-100 mN;maximum test depth: 10 µm; holding time: 10 s; loading speed:2.6 mN/s; and tip angle of the indenter: 100◦.

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198 J. LI ET AL.

0.0 0.1 0.2 0.3 0.4 0.5 0.60

5

10

15

20

25 Ni-based alloy

Molybdenized alloy

Hard

ne

ss, G

Pa

Depth, µm

Ni-base alloy

Molybdenized Ni

(a)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

20

40

60

80

100(b)

Forc

e,

mN

Displacement, µm

Molybdenized

S

h

Original

Fig. 7—Ultra-micro hardness (a) and force-displacement curves (b) ofmolybdenized layer.

The elastic modulus (E) of the specimen in the indentationtechnique has the following relationship documented by Oliverand Pharr (18):

E =√

π

2S√A

[1]

where S is the initial slope of the unloading curve. A is the area ofindent at the peak load, which is deduced by A = 26.43h2, whereh is the displacement; for example, as shown in Fig. 7(b) andFig. 15.

Friction and Wear Test

The friction and wear tests were conducted on a MG2000 hightemperature ball-on-disk tribometer (Beilun Corp.). The aluminaceramic ball (�12.7 mm, Ra 0.05 µm) was used as the upper sam-ple, while the untreated, textured, molybdenized, and duplex-treated nickel-base alloys were used as the lower samples. Thefriction tests were carried out under a load of 20 N, a sliding ve-locity of 0.4 m/s, and the furnace temperatures of 25, 200, 400,and 600◦C. The sliding distance in each test was 300 m, whichwas produced by 3000 cycles of disk rotation. The wear mass wasweighed by an analytical balance with precision of 0.1 mg beforeand after each test. The profiles of the worn tracks were mea-sured by Perthometer surface profilometer (Germany). The wornmorphologies were observed by BMX Olympus microscope andSEM. The worn dimple was analyzed by Thermo-ESCALAB250X-ray photoelectron spectroscopy (XPS).

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Frictio

n c

oeffic

ient

Sliding distance, m

1 Un-treated

2 Textured

3 Molybenized

4 Textured+Molybdenized

1

2

3

4

(a)

0.0

0.2

0.4

0.6

0.8

1.0

Fri

ction c

oeffic

ient

Sliding distance, m

1 Un-treated

2 Textured

3 Molybdenized

4 Textured+Molybdenized

(b)

1

2

3

4

0 50 100 150 200 250 300

0 50 100 150 200 250 300

0 50 100 150 200 250 300

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0F

riction

coe

ffic

ien

t

Sliding distance, m

1 Un-treated

2 Textured

3 Molybdenized

4 Textured+molybdenized

(c)

1

23

4

0 50 100 150 200 250 3000.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Fri

ctio

n c

oe

ffic

ient

Sliding distance,m

1 Un-treated

2 Textured

3 Molybdenized

4 Textured+Molybdenized

1

2

34

(d)

Fig. 8—Friction coefficient vs. sliding distance of untreated, textured,molybdenized, and duplex-treated Ni-base alloy at (a) RT; (b)200◦C; (c) 400◦C; (d) 600◦C.

RESULTS AND DISCUSSION

Morphologies of Molybdenized Texture

Figure 2 shows the surface morphology of the molybdenizedtexture. There are plate-like particles on the plane area, whichis due to the deposition of molybdenum. The bulges around the

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Tribological Properties of Laser Surface Texturing 199

0 100 200 300 400 500 6000.2

0.3

0.4

0.5

0.6F

rictio

n co

effic

ient

Temperature,

Un-treated Textured Molybdenized Textured+Molybdenized

(a)

0 100 200 300 400 500 600

10

Wea

r ra

te,1

0-5m

m3 /N

m

Temperature,

Un-treated Textured Molybdenized Textured+Molybdenized

(b)

Fig. 9—Friction coefficient (a) and wear rate (b) of untreated, textured,molybdenized, and duplex treated Ni-base alloy varied withtemperature.

dimples (Fig. 2(b)) were like unmolybdenized dimples althoughtheir sizes are decreased.

Figure 3 shows the SEM of the cross section of the duplex-treated alloy. The molybdenized layer is about 20 µm in thick-ness. The content of molybdenum decreases gradually along thedepth (Table 1).

Figure 4 shows the EDS analysis of elements in the molyb-denized dimple. The content of the molybdenum element in thedimples is lower than that on the plane area. Glow discharge oc-curred at the bulges at the brim of dimple and the molybdenumions were impeded. Figure 5 shows the XRD results of the molyb-denized layer. The molybdenized layer consisted of the nickel-base solid solution and the molybdenum deposited phase.

The depth of the molybdenized dimple is less than that of theoriginal dimples and the heights of the bulges on their brim aredecreased from 10 to 2 µm after molybdenizing (Fig. 6) due tothe ion bombardment. Figure 6(c) compares the profile curvesof the textured and the duplex-treated dimple. The depth of thedimple decreases from 47.0 to 24.5 µm after molybdenizing.

Mechanical Properties of Molybdenized Layer

Figure 7 (a) shows the ultra-micro hardness of the untreatedand the molybdenized layer. The ultra-micro hardness at the toplayer reaches 15 GPa and its ultra-micro hardness decreases withthe increase of depth. Figure 7(b) shows the load-displacementcurves of molybdenized and untreated alloy during the load-

Fig. 10—Optical morphologies of worn surface of molybdenized andtextured Ni-base alloy at 600◦C: (a) textured; (b) textur-ing/molybdenizing duplex-treated.

unload procedure. The elastic modulus is deduced from the load-displacement curves by the Oliver and Pharr formula. The elasticmodulus of the Ni-base alloy increases from 436 to 541 GPa aftermolybdenizing.

Friction and Wear Properties of Textured/MolybdenizedLayer

Figure 8 shows the curves of the friction coefficient of theuntreated, textured, molybdenized, and duplex-treated alloy asa function of sliding distance at RT to 600◦C. The friction co-efficients of the duplex-treated alloy are lower than that of thetextured or the molybdenized alloy at 200 and 400◦C, while itis comparable with those of the molybdenized layer at RT and600◦C. The textured and molybdenized duplex-treated layer pre-sented the low friction coefficient because the textured dimplestore molybdenum oxide.

Figures 9 (a)-(b) show the curves of the friction coefficientand wear rate of untreated, textured, molybdenized, and duplex-treated alloy as a function of temperature. The friction coefficient

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200 J. LI ET AL.

Fig. 11—Optical morphologies of worn surfaces of textur-ing/molybdenizing duplex-treated layer: (a) RT and (b)600◦C.

plot is the average value as shown in Figs. 8(a)-(d). At room tem-perature, the friction coefficient is little affected by texturing butit is reduced significantly by molybdenizing. However, at 600◦C,the friction coefficient of the nickel-base alloy is little affectedby molybdenizing but it is reduced by texturing (Fig. 9(a)). Thefriction coefficient is about 0.34 after texturing/molybdenizing du-plex treatment, which is comparable with that of the single molyb-denized layer.

The friction coefficient is reduced by texturing, while the fric-tion coefficient is decreased by molybdenizing due to the lowshear force of molybdenum and its oxide. The relatively higherfriction coefficient of the molybdenized layer at 600◦C corre-sponds to the friction coefficient (0.3) of MoO3.

In Fig. 9(b), at the temperature below 600◦C, the wear rate isdecreased by texturing due to the dimples storage of the wear de-bris, while molybdenizing increases the wear rate because of thelow shear force of the molybdenum layer. However, molybdeniz-ing is helpful for the reduction of the wear rate at 600◦C becauseof the formation of lubricious oxide. The wear rate of the duplex-treated layer at 600◦C is much lower than those of the untreatedand the single treated molybdenized or textured sample due to

0.0 0.5 1.0 1.5 2.0 2.5

-10

-5

0

5

10

Hei

ght,

µm

Position, mm

1 Texture2 Texture+Molybdenizing

RT(a)

1

2

Wear track

0.5 1.0 1.5 2.0 2.5

-8

-4

0

4

8

12

Hei

ght,

µm

Position, mm

1 Texture2 Texture+Molybdenizing

600(b)

1

2Wear track

Fig. 12—Profile curves of worn track of textured and texturing/molybdenizing duplex-treated Ni-base alloy: (a) RT and (b)600◦C.

the micro-dimples storage of the lubricious oxides of molybde-num (Aouadi, et al. (19)).

Figure 10 shows the optical micrographs of the textured andduplex-treated surface after rubbing against Al2O3 at 600◦C. Thewear track of the textured alloy (Fig. 10(a)) is much wider thanthat on the textured/molybdenized alloy (Fig. 10(b)). The dim-ples on the worn surface are worn out partly, while the dimpleson the duplex-treated layer maintained their original shape. Themolybdenized layer reduces wear at high temperature.

Figures 11(a)-(b) show the optical morphologies of the wornsurface of texturing/molybdenizing duplex-treated alloy afterrubbing against Al2O3 at room temperature and 600◦C. Afterrubbing for 300 m, the dimples on the worn surface of the tex-turing/molybdenizing layer are filled with wear particles at roomtemperature and 600◦C.

Figure 12 shows the profile curves of the worn track ontexturing and texturing/molybdenizing duplex-treated layers atroom temperature and 600◦C. At room temperature, the depthof the worn track on the duplex-treated layer is a little higherthan that on the textured surface, while it is in reverse at600◦C.

Figures 13(a)-(b) show SEM morphologies of the worn sur-face of the molybdenized and duplex-treated layer after rubbingagainst Al2O3 at 600◦C. The wear track of the molybdenized al-loy is covered with oxide films. The dimple on the duplex-treatedlayer is slightly plastically deformed. There are wear particles in

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Tribological Properties of Laser Surface Texturing 201

Fig. 13—SEM microscopy and EDS analysis of worn surface of tex-tured/molybdenized layer on Ni-base alloy at 600◦C: (a) molyb-denized; (b) duplex-treated; (c) EDS analysis of element in theworn dimple of duplex-treated layer.

the dimples. The EDS analysis of the dimple is shown in Fig. 13(c)and Table 2. The molybdenum and oxygen element contents areobviously higher after wear at 600◦C. The XPS analysis of theworn dimples at 600◦C (Fig. 14) shows that MoO3 existed in thedimples on the worn surface.

TABLE 2—EDS ANALYSIS OF ELEMENT IN ORIGINAL DIMPLE AND

WORN DIMPLES AT 600◦C

Element (wt%) Ni Fe Cr Mo Si O C

Original dimples 56.11 8.34 15.51 17.45 2.59 — —Worn dimples 26.43 14.56 8.69 18.83 9.83 19.71 1.95

240 235 230 225

15300

15600

15900

16200

16500

16800

Cou

nts,

s-1Binding energy, eV

Mo 3d(a)

542 540 538 536 534 532 530 528 52618000200002200024000260002800030000320003400036000

Cou

nts,

s-1

Binding energy, eV

O 1s(b)

Fig. 14—EDS analysis of element in the dimple on the worn surface ofduplex-treated layer at 600◦C:(a) Mo; (b) O.

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

20

40

60

80

100

120 1 Molybdenizing 2 Wear track of molybdenizing

For

ce, m

N

Displacement, µm

1 2

Sh

Fig. 15—Force-displacement curves of wear track of textured and molyb-denized layer at 600◦C under ultra-micro indenter.

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202 J. LI ET AL.

Fig. 16—SEM morphology (a) and XRD analysis (b) of worn surface of tex-turing and molybdenizing duplex-treated Ni-base alloy at 600◦C.

Figure 15 shows the force-displacement curves during the loadand the unload procedure under ultra-micro indenter at the loadof 100 mN. The elastic modulus is calculated from the Oliver andPharr formula (18). After wear at high temperature, the elasticmodulus of the molybdenized layer decreases from 541 GPa to393 GPa. After wear, the surface is covered by oxide films withlow elastic modulus.

Figure 16(a) shows the SEM morphology of the worn surfaceof the duplex-treated alloy after friction at 600◦C. The surfacetexture on the molybdenized layer keeps its original shape, butthe width and depth all decrease after wear at high temperature.Figure16(b) shows the XRD analysis of the worn surface of theduplex-treated alloy after 600◦C friction. There are MoO3 andCrO2 on the frictional surface, in which MoO3 is lubricious andCrO2 is abrasive (Aouodi, et al. (19); Peterson, et al. (20)).

CONCLUSIONS

1. Surface molybdenizing was performed on the laser surfacetextured Ni-base alloy. The dimples are 150–200 µm in diame-ter and 45–50 µm in depth. The molybdenized layer is approx-imately 20 µm in thickness.

2. At room temperature, the friction coefficient is reduced bymolybdenizing. However, at 600◦C, the friction coefficient ofthe nickel-base alloy is reduced by texturing. After texturing

and the molybdenizing duplex treatment, the friction coeffi-cients of the nickel-base alloy decrease from 0.40 to 0.26–0.34from room temperature to 600◦C.

3. The wear rate at temperature below 600◦C is decreased bytexturing due to the dimples storage of the wear debris. Themolybdenizing is helpful for the reduction of the wear rate at600◦C because of the formation of lubricious oxide. The wearrate of the duplex-treated layer at 600◦C is much lower thanthose of the untreated and single-treated sample due to thedimples storage of the oxides of molybdenum.

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