Kazuhisa Miyoshi

Glenn Research Center, Cleveland, Ohio

Masanori Iwaki, Kenichi Gotoh, Shingo Obara, and Kichiro Imagawa

Tsukuba Space Center, Tsukuba, Ibaraki, Japan

Friction and Wear Properties of Selected

Solid Lubricating Films

Part 3: Magnetron-Sputtered and Plasma-Assisted,

Chemical-Vapor-Deposited Diamondlike Carbon Films

NASA/TM—2000-209088/PART 3

June 2000
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National Aeronautics and

Space Administration

Glenn Research Center

Kazuhisa Miyoshi

Glenn Research Center, Cleveland, Ohio

Masanori Iwaki, Kenichi Gotoh, Shingo Obara, and Kichiro Imagawa

Tsukuba Space Center, Tsukuba, Ibaraki, Japan

NASA/TM—2000-209088/PART 3

Friction and Wear Properties of Selected

Solid Lubricating Films

Part 3: Magnetron-Sputtered and Plasma-Assisted,

Chemical-Vapor-Deposited Diamondlike Carbon Films
Available from

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This research activity was basic research conducted under the Reimbursable Space Act Agreement

between NASA Glenn Research Center and K Systems Corporation for Measurements and

Analysis of Aerospace Tribology for Various Materials.

Acknowledgment
NASA/TM—2000-209088/PART 3 1

FRICTION AND WEAR PROPERTIES OF SELECTED SOLID

LUBRICATING FILMS

Part 3: Magnetron-Sputtered and Plasma-Assisted, Chemical-Vapor-Deposited

Diamondlike Carbon Films

Kazuhisa Miyoshi

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Masanori Iwaki, Kenichi Gotoh, Shingo Obara, and Kichiro Imagawa

National Space Development Agency of Japan

Tsukuba Space Center

Tsukuba, Ibaraki 305–8505 Japan

SUMMARY

To evaluate commercially developed dry solid film lubricants for aerospace bearing applications, an investigation was conducted to examine the friction and wear behavior of magnetron-sputtered diamondlike carbon (MS

DLC) and plasma-assisted, chemical-vapor-deposited diamondlike carbon (PACVD DLC) films in sliding contact

with 6-mm-diameter American Iron and Steel Institute (AISI) 440C stainless steel balls. Unidirectional sliding friction experiments were conducted with a load of 5.9 N (600 g), a mean Hertzian contact pressure of 0.79 GPa (maximum Hertzian contact pressure of 1.2 GPa), and a sliding velocity of 0.2 m/s. The experiments were conducted at

room temperature in three environments: ultrahigh vacuum (vacuum pressure, 7×10–7 Pa), humid air (relative

humidity, ~20 percent), and dry nitrogen (relative humidity, <1 percent). The resultant films were characterized by

scanning electron microscopy, energy-dispersive x-ray spectroscopy, and surface profilometry.

Marked differences in the friction and wear of the DLC films investigated herein resulted from the environmental conditions. The main criteria for judging the performance of the DLC films were coefficient of friction and

wear rate, which had to be less than 0.3 and on the order of 10–6 mm3/N·m or less, respectively. MS DLC films and

PACVD DLC films met the criteria in humid air and dry nitrogen but failed in ultrahigh vacuum, where the coefficients of friction were greater than the criterion, 0.3. In sliding contact with 440C stainless steel balls in all three

environments the PACVD DLC films exhibited better tribological performance (i.e., lower friction and wear) than

the MS DLC films. All sliding involved adhesive transfer of wear materials: transfer of DLC wear debris to the

counterpart 440C stainless steel and transfer of 440C stainless steel wear debris to the counterpart DLC film.

INTRODUCTION

Diamondlike carbon (DLC) can be divided into two closely related categories known as amorphous,

nonhydrogenated DLC (a-DLC or a-C) and amorphous, hydrogenated DLC (H–DLC or a-C:H) (ref. 1). H–DLC

contains a variable and appreciable amount of hydrogen. DLC can be considered as a metastable carbon produced as

a thin film with a broad range of structures (primarily amorphous with variable sp2/sp3 bonding ratio) and compositions (variable hydrogen concentration). A DLC’s properties can vary considerably as its structure and composition

vary (refs. 2 to 5). Although it is a complex engineering job, it is often possible to control and tailor the properties

of a DLC to fit a specific application and thus ensure its success as a tribological product. However, such control

demands a fundamental understanding of the tribological properties of DLC films. The absence of this understanding can act as a brake in applying DLC to a new product and in developing the product.

Tribological applications of DLC coatings and films are already well established in a number of fast-growing

markets, such as magnetic recording media, high-density magnetic recording disks and sliders (heads), process

equipment (e.g., copy machines and digital video camcorders), abrasion-resistant optical products, medical devices,

implant components (including hip joints and knee implants), packaging materials, electronic devices, plastic molds,

gear pumps, stamping devices, forming dies, blades (e.g., razor blades and scalpel knives), engine parts (e.g.,
NASA/TM—2000-209088/PART 3 2

gudgeon pins), washers (e.g., grease-free ceramic faucet valve seats), seals, valves, gears, bearings, bushings, tools,

and wear parts (refs. 6 to 9). The cost is generally similar to that of carbide or nitride films deposited by CVD or

physical vapor deposition (PVD) techniques. The surface smoothness, high hardness, low coefficient of friction,

low wear rate, and chemical inertness of DLC coatings and films, along with little restriction of geometry and size,

make them well suited as solid lubricants for applications involving wear and friction.

In parts 1 and 2 of the investigation (refs. 10 and 11), four types of selected solid lubricating film were examined in ultrahigh vacuum, in humid air at a relative humidity of approximately 20 percent, and in dry nitrogen

at a relative humidity of less than 1 percent. The four types were bonded molybdenum disulfide (MoS2) films,

magnetron-sputtered MoS2 films, ion-plated silver films, and ion-plated lead films.

The present investigation (part 3) was conducted to examine the friction and wear properties of magnetronsputtered diamondlike carbon (MS DLC) and plasma-assisted, chemical-vapor-deposited diamondlike carbon

(PACVD DLC) films in the same manner as in the parts 1 and 2 investigations. Both MS DLC and PACVD DLC

films can be considered as a-DLC (amorphous, nonhydrogenated DLC). Magnetron sputtering and plasma-assisted

CVD permit close control of film deposition and thickness, can provide good adhesion to the substrate, and can

produce multilayer coatings. Unidirectional pin-on-disk sliding friction experiments were conducted with 440C

stainless steel balls in sliding contact with the solid lubricating films at room temperature in ultrahigh vacuum

(7×10–7 Pa), in humid air (relative humidity, ~20 percent), and in dry nitrogen (relative humidity, <1 percent). The

resultant solid lubricating films and their wear surfaces were characterized by scanning electron microscopy (SEM),

energy-dispersive x-ray spectroscopy (EDX), and surface profilometry. SEM and EDX were used to determine the

morphology and elemental composition of wear surfaces, wear debris, and wear of the balls. The sampling depth of

EDX for elemental information ranged between 0.5 and 1 μm in this investigation. Surface profilometry was used to

determine the surface morphology, roughness, and wear of the coatings.

SELECTED MATERIALS

Three specimens of each film type, MS DLC and PACVD DLC, produced on 440C stainless steel disk substrates were used in this investigation (table I). The MS DLC films had a multilayer structure and were prepared

using two chromium targets, 6 tungsten carbide (WC) targets, and methane (CH4) gas. Each multilayer film comprised WC layers (20 to 50 nm thick) alternating with carbon layers (20 to 50 nm thick). The Vickers hardness number was approximately 1000. The 2- to 3-μm-thick MS DLC films were relatively smooth, and their

centerline-average roughness Ra, measured using a cutoff of 1 mm, was 43 nm with a standard deviation of 5.1 nm.

The PACVD DLC films were prepared using radiofrequency plasma and consisted of two layers. Each film

comprised an approximately 2-μm-thick DLC layer on an approximately 2-μm-thick silicon-DLC underlayer. The

top DLC layer was deposited using CH4 gas at a total pressure of 8 Pa with a power of 1800 to 2000 W at –750 to

–850 V for 120 min. The silicon-containing DLC underlayer was deposited using a mixture of CH4 and C4H12Si

(tetramethylsilane) gases. The ratio of the concentrations of CH4 and C4H12Si used was 90:18 (std cm3/min) at a

total pressure of 10 Pa with a power of 1800 to 2000 W at –850 to –880 V for 60 min. The Vickers hardness number

was 1600 to 1800. The 3- to 5-μm-thick PACVD DLC films were also relatively smooth and their Ra, measured

using a cutoff of 1 mm, was 29 nm with a standard deviation of 3.2 nm. The 6-mm-diameter 440C stainless steel

balls (grade number, 10) used were smooth having an Ra of 0.025 μm with a standard deviation of 0.02 μm or less.

EXPERIMENT

The pin-on-disk tribometer used in the investigation was mounted in a vacuum chamber (refs. 10 and 11).

Unidirectional pin-on-disk sliding friction experiments were conducted at room temperature in ultrahigh vacuum

(7×10–7 Pa), in humid air (relative humidity, ~20 percent), and in dry nitrogen (relative humidity, <1 percent). All

experiments were conducted with 6-mm-diameter 440C stainless steel balls in sliding contact with the DLC films

deposited on 440C stainless steel substrate disks. All experiments were conducted with a load of 5.9 N (600 g) at

the sliding velocity of 0.2 m/s. The mean Hertzian contact pressure of the 440C stainless steel substrates in contact

with the 440C stainless steel balls was approximately 0.79 GPa (maximum Hertzian contact pressure, 1.2 GPa). The

pin-on-disk tribometer can measure friction in vacuum, in humid air, and in dry nitrogen during sliding. The friction

force was continuously monitored during the sliding friction experiments.
NASA/TM—2000-209088/PART 3 3

The sliding wear life (film wear life or film endurance life) for the coatings in this investigation was determined

to be the number of passes at which the coefficient of friction rose to 0.3 in a given environment. Wear was quantified by measuring the wear scars and wear tracks on the specimens after the wear experiments. Film wear volumes

were obtained by averaging the cross-sectional areas, determined from stylus tracings, measured across the wear

tracks at a minimum of four locations in each wear track. Then, the average cross-sectional area of the wear track

was multiplied by the wear track length. The wear rate, known as the dimensional wear coefficient, is defined as the

volume of material removed at a unit load and in a unit sliding distance expressed as cubic millimeters per

newton·meter.

RESULTS AND DISCUSSION

Friction Behavior

Figures 1 to 3 present typical friction traces obtained in ultrahigh vacuum, in humid air, and in dry nitrogen,

respectively, for the MS DLC and PACVD DLC films in sliding contact with 440C stainless steel balls as a function

of the number of passes. All the friction traces for the DLC films obtained in the three environments fluctuated. In

ultrahigh vacuum (fig. 1) the coefficient of friction for both the MS DLC and PACVD DLC films rose to 0.3 in a

few passes; the steady-state values were approximately 0.7 for the MS DLC films and 0.54 for the PACVD DLC

films. In humid air (fig. 2) the coefficients of friction for both the MS DLC and PACVD DLC films decreased

to approximately 0.1; the steady-state value for the PACVD DLC films was generally lower than that for the MS

DLC films. In dry nitrogen (fig. 3) the coefficient of friction for the MS DLC films increased to 0.3 at approximately

24 000 passes, and the steady-state coefficient of friction for the PACVD DLC films decreased to 0.05 at 300 000

passes.

Comparing the data taken in the different environments (figs. 1 to 3) shows that the coefficients of friction for

both the MS DLC and PACVD DLC films were much higher in ultrahigh vacuum than in humid air and in dry nitrogen. The coefficients of friction of the PACVD DLC films were generally lower than those of the MS DLC films in

all three environments.

Wear Behavior

Figures 4 to 6 present SEM photomicrographs of wear tracks on the MS DLC and PACVD DLC films deposited on 440C stainless steel disks and the wear scars on the 440C stainless steel balls in ultrahigh vacuum, in humid

air, and in dry nitrogen, respectively. The SEM observations were made at 1000 passes in ultrahigh vacuum, at

300 000 passes in humid air, and either at the end of film wear life or at 300 000 passes in dry nitrogen. In ultrahigh

vacuum (fig. 4) the sliding action roughened the entire wear tracks of the MS DLC films at 1000 passes but locally

produced micro-pits in the wear tracks of the PACVD DLC films. With both films types in ultrahigh vacuum, wear

debris particles and agglomerated wear debris were generated during sliding. In humid air the sliding action generated smooth wear surfaces on the MS DLC films and deposited a large amount of agglomerated, pasty wear debris

on the wear scars of the 440C stainless steel balls (fig. 5(a)). In humid air the sliding action generated a smooth wear

surface on the PACVD DLC films with relatively large wear debris particles (fig. 5(b)). In dry nitrogen the sliding

action generated a smooth wear surface for both film types and produced fine wear debris particles with the MS

DLC films (fig. 6(a)) and relatively large wear debris particles with the PACVD DLC films (fig. 6(b)).

The wear scars on the 440C stainless steel balls were generally smooth, regardless of the environment. Thin,

smeared wear patches and particles of the DLC films generally covered the smooth wear scars. Smeared tongues of

thin, layered, agglomerated wear debris were also present. Most of the loose and smeared wear debris accumulated

outside the wear scars.

Wear (Endurance) Life

As in parts 1 and 2 of the investigation (refs. 10 and 11) the sliding wear (endurance) life of the solid lubricating

films deposited on 440C stainless steel disks was determined to be the number of passes at which the coefficient of
NASA/TM—2000-209088/PART 3 4

friction rose to 0.3. The sliding wear lives of the DLC films examined in this investigation (table II) varied with the

environment. When judged by the coefficient of friction, the wear lives of both film types were extremely short in

ultrahigh vacuum. The MS DLC films had much longer wear lives in humid air than in dry nitrogen and in ultrahigh

vacuum. The PACVD DLC films had much longer wear lives in humid air and in dry nitrogen than in ultrahigh

vacuum.

Comparison of Steady-State Coefficients of Friction and Wear Rates

Table II also presents the steady-state coefficients of friction and the film and ball wear rates after sliding contact in all three environments. The data presented in the table reveal the marked differences in coefficient of friction

resulting from the environmental conditions. Both the MS DLC and PACVD DLC films had high coefficients of

friction, high film wear rates, and high ball wear rates in ultrahigh vacuum but relatively low coefficients of friction,

low film wear rates, and low ball wear rates in humid air and in dry nitrogen. Both film types met the main criteria

for judging the tribological performance of films (coefficient of friction less than 0.3 and wear rate on the order

of 10–6 mm3/N·m or less) in humid air and in dry nitrogen. In sliding contact with a 440C stainless steel ball the

PACVD DLC films exhibited better tribological performance (i.e., lower friction and wear) than did the MS DLC

films in all three environments.

Sliding Wear, Wear Debris, and Transferred Wear Fragments

Examining the morphology and composition of the worn surfaces of MS DLC and PACVD DLC films in

sliding contact with 440C stainless steel balls by SEM and EDX provided detailed information about plastic deformation of the DLC films, wear debris, and transferred wear fragments produced during sliding (figs. 7 to 12). All

sliding involved generation of fine wear debris particles and agglomerated wear debris and transfer of the worn

materials.

Ultra-high-vacuum environment.—Figure 7(a) presents a typical wear track on an MS DLC film over which

a 440C stainless steel ball has passed in ultrahigh vacuum leaving a roughened worn DLC film surface and a small

amount of transferred steel wear fragments. The wear scar on the counterpart 440C stainless steel ball (fig. 7(b))

contained fine steel wear debris particles and a small amount of transferred DLC wear fragments. The wear mechanism for an MS DLC film in sliding contact with a 440C stainless steel ball in ultrahigh vacuum is that of small

DLC fragments chipping off the surface.

Figure 8(a) presents a typical wear track on a PACVD DLC film over which a 440C stainless steel ball has

passed in ultrahigh vacuum leaving smeared, agglomerated DLC wear debris and a small amount of transferred

steel wear fragments. The wear scar on the counterpart 440C stainless steel ball (fig. 8(b)) contained fine steel wear

debris particles and large smeared, agglomerated wear debris patches containing transferred DLC wear fragments.

The wear mechanism for a PACVD DLC film in sliding contact with a 440C stainless steel ball in ultrahigh vacuum

was adhesion, and plastic deformation played a role in the burnished appearance of the agglomerated wear debris.

Humid-air environment.—Figure 9(a) presents a typical wear track on an MS DLC film over which a 440C

stainless steel ball has passed in humid air leaving a small amount of transferred steel wear fragments. The fine

asperities of the MS DLC film were flattened and elongated in the sliding direction by plastic deformation, revealing

a smooth, burnished appearance. The entire wear scar on the counterpart 440C stainless steel ball (fig. 9(b)) contained thick transferred layers (or sheets) of MS DLC. Plate-like DLC wear debris particles were found at the edges

of the wear scar. Severe plastic deformation and shearing occurred in the DLC film during sliding.

Figure 10(a) presents a typical wear track on a PACVD DLC film over which a 440C stainless steel ball has

passed in humid air leaving a small amount of transferred steel wear fragments. The fine asperities of the PACVD

DLC film were flattened and elongated in the sliding direction by plastic deformation, revealing a smooth, burnished

appearance. The smooth wear scar on the counterpart 440C stainless steel ball (fig. 10(b)) contained an extremely

small amount of transferred PACVD DLC wear debris.

Dry-nitrogen environment.—Figure 11(a) presents a typical wear track on an MS DLC film over which a 440C

stainless steel ball has passed in dry nitrogen. At 23 965 passes (end of life) there was an extremely small amount of

transferred steel wear debris, and the fine asperities of the MS DLC film were flattened and elongated in the sliding

direction by plastic deformation, revealing a smooth, burnished appearance. In addition to the small amount of steel
NASA/TM—2000-209088/PART 3 5

wear debris particles, smeared, agglomerated DLC wear debris was found on the MS DLC film. Plastic deformation

occurred in the DLC film during sliding. The wear scar on the counterpart 440C stainless steel ball (fig. 11(b)) contained transferred DLC wear debris particles and patches.

Figure 12(a) presents a typical wear track on a PACVD DLC film over which a 440C stainless steel ball has

passed in dry nitrogen. At 300 000 passes DLC wear debris, micro-pits, and an extremely small amount of transferred steel wear debris were observed. The wear scar on the counterpart 440C stainless steel ball (fig. 12(b)) contained fine grooves in the sliding direction, steel wear debris, and transferred DLC wear debris.

CONCLUSIONS

To evaluate recently developed diamondlike carbon (DLC) film lubricants for aerospace bearing applications,

unidirectional sliding friction experiments were conducted with DLC films in sliding contact with AISI 440C

stainless steel balls in ultrahigh vacuum, in humid air, and in dry nitrogen. The main criteria for judging the performance of the DLC films were coefficient of friction and wear rate, which had to be less than 0.3 and on the order of

10–6 mm3/N·m or less, respectively. The following conclusions were drawn:

1. Magnetron-sputtered (MS) DLC films and plasma-assisted, chemical-vapor-deposited (PACVD) DLC films met

the criteria in humid air and in dry nitrogen but failed in ultrahigh vacuum, where the coefficients of friction

were greater than the criterion, 0.3.

2. In sliding contact with a 440C stainless steel ball the PACVD DLC films exhibited better tribological performance (i.e., lower friction and wear) in all three environments than the MS DLC films.

3. All sliding involved adhesive transfer of wear materials: transfer of DLC wear debris to the counterpart 440C

stainless steel ball and transfer of 440C stainless steel wear debris to the counterpart DLC film.

REFERENCES

1. Pierson, H.O.: Handbook of Carbon, Graphite, Diamond, and Fullerenes: Properties, Processing, and Applications. Noyes Publications, Park Ridge, NJ, 1993.

2. Pouch, J.J.; and Alterovitz, S.A., eds.: Properties and Characterization of Amorphous Carbon Films. Materials

Science Forum, Vols. 52 and 53, Trans Tech Publications, Switzerland, 1990.

3. Miyoshi, K.; Pouch, J.J.; and Alterovitz, S.A.: Plasma-Deposited Amorphous Hydrogenated Carbon Films and

Their Tribological Properties. Properties and Characterization of Amorphous Carbon Films, J.J. Pouch and

S.A. Alterovitz, eds., Materials Science Forum, Vols. 52 and 53, Trans Tech Publications, Switzerland, 1990,

pp. 645–656.

4. Wu, R.L.C.; Miyoshi, K.; Vuppuladhadium, R.; and Jackson, H.E.: Physical and Tribological Properties of

Rapid Thermal Annealed Diamond-like Carbon Films. Surface and Coatings Technology, vol. 55, 1992,

pp. 576–580.

5. Miyoshi, K.; et al.: Sliding Wear and Fretting Wear of Diamondlike Carbon-Based, Functionally Graded

Nanocomposite Coatings. Wear, vol. 229, 1999, pp. 65–73.

6. Molloy, A.P.; and Dionne, A.M., eds., World Markets, New Applications, and Technology for Wear and

Superhard Coatings. Gorham Advanced Materials, Inc., Gorham, ME, 1998.

7. Miyoshi, K.: Lubrication by Diamond and Diamondlike Carbon Coatings. J. Tribology, vol. 120, no. 2, 1998,

pp. 379–384.

8. Miyoshi, K.; et al.: CVD Diamond, DLC, and c-BN Coating for Solid Film Lubrication. Tribology Letters,

vol. 5, 1998, pp. 123–129.

9. Miyoshi, K.: Tribological Characteristics and Applications of Superhard Coatings: CVD Diamond, DLC, and

c-BN. Proceedings of Applied Diamond Conference/Frontier Carbon Technology Joint Conference 1999,

Tsukuba, Japan (adc99@icube-t.co.jp). (Also NASA TM—1999-209189.)

10. Miyoshi, K.; et al.: Friction and Wear Properties of Selected Solid Lubricating Films, Part I: Bonded and

Magnetron-Sputtered Molybdenum Disulfide and Ion-Plated Siver Films. NASA/TM—1999-209088/

PART 1, 1999.

11. Miyoshi, K.: Friction and Wear Properties of Selected Solid Lubricating Films, Part 2: Ion-Plated Lead Films.

NASA TM—2000-209088/PART 2, 2000.
NASA/TM—2000-209088/PART 3 6

TABLE I.—CHARACTERISTICS OF SELECTED SOLID

LUBRICATING FILMS

[Film material, carbon; substrate material, 440C stainless steel.]

Surface roughness of films,

Ra,

nm

Film type Film

thickness,

mm

Mean Standard

deviation

Magnetron-sputtered

diamondlike carbon (MS DLC)

2–3 43 5.1

Plasma-assisted, chemicalvapor-deposited diamondlike

carbon (PACVD DLC)

3–5 29 3.2

TABLE II.—STEADY-STATE COEFFICIENT OF FRICTION, WEAR LIFE,

AND WEAR RATES FOR DLC FILMS IN SLIDING CONTACT WITH

440C STAINLESS STEEL BALLS

Film Environment Steady-state

coefficient of

friction

Film wear

(endurance)

lifea

Film wear

rate,

mm3/N◊m

Ball wear

rate,

mm3/N◊m

Magnetronsputtered DLC

Vacuum

Air

Nitrogen

0.70

0.12

0.12

<10

>3¥105

23 965

5.7¥10– 5

1.7¥10– 7

4.2¥10– 7

3.2¥10– 4

4.1¥10– 8

1.1¥10– 7

Plasma-assisted

CVD DLC

Vacuum

Air

Nitrogen

0.54

0.07

0.06

<10

>3¥105

>3¥105

1.1¥10– 5

1.0¥10– 7

1.1¥10– 8

1.8¥10– 4

2.3¥10– 8

6.4¥10– 9

aFilm wear life is determined to be the number of passes at which the coefficient of

 friction rose to 0.3.
NASA/TM—2000-209088/PART 3 7

Figure 1.—Friction traces for (a) MS DLC film and

 (b) PACVD DLC film in sliding contact with 440C

 stainless steel balls in ultrahigh vacuum.

0.8

Number of passes

Coefficient of friction

0 2 4 6 8 10x102

0

0.2

0.6

0.4

0

Number of passes

Coefficient of friction

02468 10x102

0.2

0.6

0.4

0.8

(a)

(b)

Figure 2.—Friction traces for (a) MS DLC film and

 (b) PACVD DLC film in sliding contact with 440C

 stainless steel balls in humid air.

Number of passes

0 0.6 1.2 1.8 2.4 3.0x105

0

0.2

0.4

(b)

Coefficient of

friction

0

Number of passes

Coefficient of

friction

0 0.6 1.2 1.8 2.4 3.0x105

0.2

0.4

(a)

Figure 3.—Friction traces for (a) MS DLC film and

 (b) PACVD DLC film in sliding contact with 440C

 stainless steel balls in dry nitrogen.

Number of passes

Coefficient of

friction

0 0.6 1.2 1.8 2.4 3.0x105

0

0.2

0.4

(b)

0

Number of passes

Coefficient of friction

0 0.6 1.2 1.8 2.4

0 0.6 1.2 1.8 2.4x104

3.0x105

0.2

0.6

0.4

0.8

0

0.2

0.6

0.4

0.8

(a)
NASA/TM—2000-209088/PART 3 8

Figure 4.—Wear tracks and wear scars in ultrahigh vacuum at 1000 passes. (a) Materials pair of MS DLC film and

 440C stainless steel ball. (b) Materials pair of PACVD DLC film and 440C stainless steel ball.

100 μm

100 μm

(a) Sliding direction

(b) Sliding direction

100 μm

100 μm

Film wear track Ball wear scar
NASA/TM—2000-209088/PART 3 9

Figure 5.—Wear tracks and wear scars in humid air at 300 000 passes. (a) Materials pair of MS DLC film and

 440C stainless steel ball. (b) Materials pair of PACVD DLC film and 440C stainless steel ball.

100 μm

100 μm

(a) Sliding direction

(b) Sliding direction

100 μm

100 μm

Film wear track Ball wear scar
NASA/TM—2000-209088/PART 3 10

Figure 6.—Wear tracks and wear scars in dry nitrogen. (a) Materials pair of MS DLC film and 440C stainless

 steel ball at 23 965 passes. (b) Materials pair of PACVD DLC film and 440C stainless steel ball at 300 000

 passes.

100 μm

100 μm

(a) Sliding direction

(b) Sliding direction

100 μm

100 μm

Film wear track Ball wear scar
NASA/TM—2000-209088/PART 3 11

Figure 7.—Morphology and elemental composition by SEM and EDX (a) of wear track produced on MS DLC

 film and (b) of wear scar produced on 440C stainless steel ball at 1000 passes in ultrahigh vacuum.

(b)

10 μm

Counts

0

0.5

Energy, keV

Ck

Crk

Fek

Sik and

Wm

1.0x105

0 6 2 12 4 10 8 14

10 μm

(a)

Counts

0

Energy, keV

0 6 2

Ck Crk Fek Nik

Wl

Sik and Wm

10 12 14

1.0x105

0.5

4 8

SEM EDX
NASA/TM—2000-209088/PART 3 12

Figure 8.—Morphology and elemental composition by SEM and EDX (a) of wear track produced on PACVD DLC 

 film and (b) of wear scar produced on 440C stainless steel ball at 1000 passes in ultrahigh vacuum.

10 μm

(a)

Counts

0

Energy, keV

0 6 2

Ck Crk Fek

Sik

10 12 14

3.0x105

1.0

0.5

2.0

2.5

1.5

4 8

10 μm

(b)

Counts

0

0.5

Energy, keV

Ck

Crk

Fek

Sik

Sk

1.0x105

0 6 2 12 4 10 8 14

SEM EDX
NASA/TM—2000-209088/PART 3 13

Figure 9.—Morphology and elemental composition by SEM and EDX (a) of wear track produced on MS DLC

 film and (b) of wear scar produced on 440C stainless steel ball at 300 000 passes in humid air.

10 μm

(a)

Counts

0

Energy, keV

0 6 2

Ck Crk Fek Nik

Wl

Sik and Wm

10 12 14

1.0x105

0.5

4 8

10 μm

(b)

Counts

0

0.5

Energy, keV

Ck

Fek

Sik and Wm 1.0x105

0 6 2 12 4 10 8 14

Cr Wl k

SEM EDX
NASA/TM—2000-209088/PART 3 14

Figure 10.—Morphology and elemental composition by SEM and EDX (a) of wear track produced on PACVD

 DLC film and (b) of wear scar produced on 440C stainless steel ball at 300 000 passes in humid air.

10 μm

(a)

Counts

0

Energy, keV

0 6 2

Ck

Crk Fek

Sik

10 12 14

2.0x105

1.0

1.5

0.5

4 8

10 μm

(b)

Counts

0

0.5

Energy, keV

Ck

Crk

Fek

Sik

Sk

1.0x105

0 6 2 12 4 10 8 14

SEM EDX
NASA/TM—2000-209088/PART 3 15

Figure 11.—Morphology and elemental composition by SEM and EDX (a) of wear track produced on MS DLC

 film and (b) of wear scar produced on 440C stainless steel ball at 23 965 passes in dry nitrogen

10 μm

Counts

0

Energy, keV

0 6 2

Ck Crk

Ark

Fek Nik

Wl

Sik and Wm

10 12 14

1.0x105

0.5

(a)

4 8

10 μm

Counts

0

0.5

Energy, keV

Ck Crk

Fek

Sik and

Wm

1.0x105

(b)

0 6 2 12 4 10 8 14

Wl

SEM EDX
NASA/TM—2000-209088/PART 3 16

Figure 12.—Morphology and elemental composition by SEM and EDX (a) of wear track produced on PACVD

 DLC film and (b) of wear scar produced on 440C stainless steel ball at 300 000 passes in dry nitrogen.

10 μm

10 μm

Counts

0

0.5

Energy, keV

Ck

Crk

Fek

Sik

Ok

1.0x105

(b)

0 6 2 12 4 10 8 14

Counts

0

Energy, keV

0 6 2

Ck

Crk Fek

Sik

10 12 14

2.5x105

0.5

(a)

1.0

1.5

2.0

4 8

SEM EDX
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NASA TM—2000-209088-

PART 3

E–12214

WU–297–60–00–00

22

A03

Lubricants

Unclassified -Unlimited

Subject Category: 27 Distribution: Nonstandard

Friction and Wear Properties of Selected Solid Lubricating Films

Part 3: Magnetron-Sputtered and Plasma-Assisted, Chemical-Vapor-Deposited

Diamondlike Carbon Films

Kazuhisa Miyoshi, Masanori Iwaki, Kenichi Gotoh, Shingo Obara,

and Kichiro Imagawa

Kazuhisa Miyoshi, NASA Glenn Research Center, Cleveland, Ohio; Masanori Iwaki, Kenichi Gotoh, Shingo Obara, and

Kichiro Imagawa, National Space Development Agency of Japan, Tsukuba Space Center, Tsukuba, Ibaraki 305–8505,

Japan. Responsible person, Kazuhisa Miyoshi, organization code 5160, (216) 433–6078.

To evaluate commercially developed dry solid film lubricants for aerospace bearing applications, an investigation was conducted to examine

the friction and wear behavior of magnetron-sputtered diamondlike carbon (MS DLC) and plasma-assisted, chemical-vapor-deposited

diamondlike carbon (PACVD DLC) films in sliding contact with 6-mm-diameter American Iron and Steel Institute (AISI) 440C stainless

steel balls. Unidirectional sliding friction experiments were conducted with a load of 5.9 N (600 g), a mean Hertzian contact pressure of

0.79 GPa (maximum Hertzian contact pressure of 1.2 GPa), and a sliding velocity of 0.2 m/s. The experiments were conducted at room

temperature in three environments: ultrahigh vacuum (vacuum pressure, 7×10–7 Pa), humid air (relative humidity, ~20 percent), and dry

nitrogen (relative humidity, <1 percent). The resultant films were characterized by scanning electron microscopy, energy-dispersive x-ray

spectroscopy, and surface profilometry. Marked differences in the friction and wear of the DLC films investigated herein resulted from the

environ-mental conditions. The main criteria for judging the performance of the DLC films were coefficient of friction and wear rate, which

had to be less than 0.3 and on the order of 10–6 mm3/N·m or less, respectively. MS DLC films and PACVD DLC films met the criteria in

humid air and dry nitrogen but failed in ultrahigh vacuum, where the coefficients of friction were greater than the criterion, 0.3. In sliding

contact with 440C stainless steel balls in all three environments the PACVD DLC films exhibited better tribological performance (i.e., lower

friction and wear) than the MS DLC films. All sliding involved adhesive transfer of wear materials: transfer of DLC wear debris to the

counterpart 440C stainless steel and transfer of 440C stainless steel wear debris to the counterpart DLC film.