NASA/TM—2000-209088/PART2

May 2000

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 2: Ion-Plated Lead Films
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NASA/TM—2000-209088/PART2

May 2000

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

Friction and Wear Properties of Selected

Solid Lubricating Films

Part 2: Ion-Plated Lead Films
Acknowledgments

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.

Available from

NASA Center for Aerospace Information

7121 Standard Drive

Hanover, MD 21076

Price Code: A03

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22100

Price Code: A03
NASA/TM—2000-209088/PART2 1

FRICTION AND WEAR PROPERTIES OF SELECTED SOLID

LUBRICATING FILMS

Part 2: Ion-Plated Lead 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 ion-plated lead 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 ion-plated lead films investigated herein resulted from

the environmental conditions. The main criteria for judging the performance of the ion-plated lead 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 ion-plated lead films met both criteria only in ultrahigh vacuum but failed in humid air and

in dry nitrogen, where the coefficient of friction was higher than the criterion. Both the lead film wear rate and

the ball wear rate met that criterion in all three environments.

Adhesion and plastic deformation played important roles in the friction and wear of the ion-plated lead

films in contact with 440C stainless steel balls in the three environments. All sliding involved adhesive transfer of materials: transfer of lead wear debris to the counterpart 440C stainless steel and transfer of 440C stainless steel wear debris to the counterpart lead.

INTRODUCTION

Soft metals have a number of properties that make them attractive as solid lubricants for special situations. For example, in addition to their low shear strengths and ability to be applied as continuous films over

harder substrates, soft metals are good conductors of heat and electricity and are stable in vacuum or when

exposed to nuclear radiation (ref. 1).

Soft metal films can be deposited as lubricating films on harder substrates by conventional electroplating

or by physical vapor deposition methods, such as evaporation, sputtering, and ion plating. Ion plating and vacuum sputtering permit close control of film deposition and thickness and can provide good adhesion to the substrate (ref. 2).

Thin-metal-film lubrication is most relevant at high temperatures or in applications where sliding is limited (e.g., rolling-element bearings). Lead (Pb) films have been very successful for long-term, rolling-element

bearing lubrication in space mechanisms (ref. 3). One advantage of lead films over those of silver or indium is

the unavoidable presence of lead oxide (PbO), a reputedly good solid lubricant, within the films (refs. 1 and

4). Ion-plated lead films are used in such mechanisms as solar array drives in European satellites (ref. 5). Lead
NASA/TM—2000-209088/PART2 2

films have been used for many years to lubricate rolling-element bearings on rotating anode x-ray tubes, on

satellite parts operating in space, and on other equipment exposed to high temperatures and nuclear radiation.

As the multidisciplinary science of lubrication, friction, and wear, tribology is application oriented, with a

rich methodology. Once the initial shortcomings relating to lubrication in design and application had been

dealt with, it became increasingly clear that materials science and technology ranked equal with design in

reducing friction and wear of machinery and mechanical components (ref. 6), particularly in the field of space

mechanisms. In modern technology, the coefficient of friction and the wear rate are regarded to be widely

variable, depending on operational variables, lubricants, substrate properties, and surface films (ref. 7). Therefore, testing is central (ref. 8), and particularly standard performance testing of solid lubricant systems is

important for the lubricant manufacturer during development of new lubricating materials, for quality control

during lubricant manufacture, and for providing quantitative criteria for manufacturing specifications.

For mechanism design engineers (i.e., users), compiling manufacturers’ standard test results for a number

of lubricant formulations can aid in selecting the best lubricant for an application. However, such data can at

best only narrow the field to a specific class of lubricants. To decide on the optimum lubricant formulation for

a specific application, more custom-design testing, element testing, component testing, and full-scale testing

are required. However, after choosing the optimum lubricant, such standard tests can also be useful for quality

control. This is especially important during a long space program, where satellites or launch vehicles are built

over a period of years, so that lubricant formulations and film application procedures might undergo change.

For solid lubricant films the end user should request that standard test coupons be coated along with the actual

parts. Testing of each lubricant batch will ensure that the manufacturing quality remains constant throughout

the life of the program.

In the part 1 of the investigation (ref. 8) three 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 three types were bonded molybdenum disulfide (MoS2) films,

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

The present investigation was conducted to examine the friction and wear properties of ion-plated lead

films in the same manner as the part 1 investigation. Unidirectional pin-on-disk sliding friction experiments

were conducted with American Iron and Steel Institute (AISI) 440C stainless steel balls in sliding contact with

the solid lubricating films at room temperature 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 resultant solid

lubricating films and their wear surfaces were characterized by scanning electron microscopy (SEM), energydispersive x-ray spectroscopy (EDX), and surface profilometry. SEM and EDX were used to determine the

morphology and elemental composition of wear surfaces and wear debris. The sampling depth of EDX for elemental information ranged between 0.5 and 1 mm in this investigation. Surface profilometry was used to determine the surface morphology, roughness, and wear of the coatings.

SELECTED MATERIALS

Three specimens of each of the two thicknesses of ion-plated lead film produced on 440C stainless steel

disk substrates were used in this investigation (table I). The 0.55-mm-thick, ion-plated lead films were

relatively smooth, and their centerline-average roughness Ra, measured using a cutoff of 1 mm, was 98 nm

with a standard deviation of 15 nm. The 0.35-mm-thick, ion-plated lead films were also relatively smooth, and

their Ra, measured using a cutoff of 1 mm, was 40 nm with a standard deviation of 9.5 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 mm or less.

EXPERIMENT

The pin-on-disk tribometer used in the investigation was mounted in a vacuum chamber (fig. 1). Unidirectional pin-on-disk sliding friction experiments were conducted in ultrahigh vacuum (7¥10–7 Pa), in humid air

(~20 percent relative humidity), and in dry nitrogen (<1 percent relative humidity) at room temperature. All

experiments were conducted with 6-mm-diameter 440C stainless steel balls in sliding contact with the ionplated lead films deposited on 440C stainless steel substrate disks. All experiments were conducted with a

load of 5.9 N (600 g) at a 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 ~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 friction experiments.
NASA/TM—2000-209088/PART2 3

The sliding wear life for the coatings (film wear life or film endurance life) 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 can be 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 2 to 4 present typical friction traces obtained in ultrahigh vacuum, in humid air, and in dry

nitrogen for the ion-plated lead films in sliding contact with 440C stainless steel balls as a function of the

number of passes. The friction traces obtained in vacuum fluctuated (fig. 2). The coefficient of friction for the

0.55-mm-thick, ion-plated lead film increased to 0.3 at 30 294 passes, and the coefficient of friction for the

0.35-mm-thick, ion-plated lead film increased to 0.3 at 21 825 passes. In humid air (fig. 3) the coefficients of

friction for both film thicknesses rose to 0.3 in a small number of passes, approximately 100. In dry nitrogen

(fig. 4) the coefficients of friction for both film thicknesses gradually increased to 0.3 at approximately 1000

passes. Comparing the data taken in different environments (figs. 2 to 4) shows that the coefficients of friction

and the endurance lives of the ion-plated lead films were much better in ultrahigh vacuum than in either humid

air or dry nitrogen.

Wear Behavior

Figures 5 to 7 present SEM photomicrographs of wear scars on 440C stainless steel balls and wear tracks

on the ion-plated lead films deposited on 440C stainless-steel disks after sliding contact in ultrahigh vacuum,

in humid air, and in dry nitrogen, respectively. The SEM observations were made either at the end of wear life,

at which the coefficient of friction rose to 0.3, or at the number of passes at which the coefficient of friction

rose to 0.5.

The wear tracks on the lead films revealed that the sliding action usually generated a smooth wear surface, fine wear-debris particles, and agglomerated, pasty wear debris, regardless of the environment. The wear

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

wear patches and particles of the lead 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 Life (Endurance Life)

As in part 1 of this investigation 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 friction

rose to 0.3 (ref. 8). The sliding wear lives of the ion-plated lead films examined in this investigation (fig. 8

and table II) varied with the environment, being much longer in ultrahigh vacuum than in dry nitrogen and in

humid air.

Comparison of Steady-State Coefficients of Friction and Wear Rates

Table II and figure 9 present the steady-state coefficients of friction, the wear rates for the ion-plated lead

films, and the wear rates for the 440C stainless steel balls after sliding contact in all three environments. The

data presented in the table reveal the marked difference in coefficient of friction resulting from the environmental conditions. Both the 0.55- and 0.35-mm-thick, ion-plated lead films had low coefficients of friction in

ultrahigh vacuum but relatively high coefficients of friction in humid air and in dry nitrogen. The coefficients

of friction investigated herein were, in ascending order, those in ultrahigh vacuum, in humid air, and in dry

nitrogen.
NASA/TM—2000-209088/PART2 4

The wear rates for the ion-plated lead films and for the counterpart 440C stainless steel balls were not susceptible to environment. The wear rates in ultrahigh vacuum were similar to those in humid air and in dry

nitrogen.

Sliding Wear, Wear Debris, and Transferred Wear Fragments

Adhesion and plastic deformation played important roles in the friction and sliding wear of the ion-plated

lead films in contact with the 440C stainless steel balls in all three environments. The worn surfaces of both

the films and the balls contained wear debris particles. Examining the morphology and compositions of the

worn surfaces by SEM and EDX provided detailed information about plastic deformation of the lead films,

wear debris, and transferred wear fragments produced during sliding (figs. 10 to 15). Marked plastic deformation occurred in the lead films. Smeared, agglomerated wear debris accumulated around the contact border,

particularly on the ends of wear scars. All sliding involved adhesive transfer of materials.

 Ultra-high-vacuum environment.æFigure 10(a) presents a typical wear track on a 0.55-mm-thick, ionplated lead film over which a 440C stainless steel ball has passed in ultrahigh vacuum leaving a small amount

of transferred steel wear fragments. The fine asperities of the ion-plated lead film were flattened and elongated

in the direction of sliding by plastic deformation, revealing a burnished appearance. Figure 11(a) presents a

typical wear track on a 0.35-mm-thick, ion-plated lead film over which a 440C stainless steel ball has passed

in ultrahigh vacuum. The wear track on the 0.35-mm-thick film was similar to that on the 0.55-mm-thick film.

The entire wear scar on the counterpart 440C stainless steel ball (figs. 10(b) and 11(b)) contained thick

transferred layers (or sheets) of lead. Plate-like lead debris particles were found at the edges of the film wear

track. Severe plastic deformation and shearing occurred in the lead film during sliding.

 Humid-air environment.æFigure 12(a) presents a typical wear track on a 0.55-mm-thick, ion-plated lead

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 ion-plated lead film were flattened and elongated in the direction of

sliding by plastic deformation, revealing a burnished appearance. Figure 13(a) presents a typical wear track on

a 0.35-mm-thick, ion-plated lead film over which a 440C stainless steel ball has passed in humid air. The wear

track on the 0.35-mm-thick film was similar to that on the 0.55-mm-thick film.

The wear scar on the counterpart 440C stainless steel ball (figs. 12(b) and 13(b)) contained an extremely

small amount of transferred lead debris particles. This result suggests that oxidation of lead during sliding in

humid air may prevent large lead transfer. In addition to the small wear debris particles, plate-like lead debris

was found at the edges of the film wear track. Severe plastic deformation and shearing occurred in the lead

film during sliding.

 Dry-nitrogen environment.æFigure 14(a) presents a typical wear track on a 0.55-mm-thick, ion-plated

lead film over which a 440C stainless steel ball has passed in dry nitrogen leaving transferred steel wear fragments. The fine asperities of the ion-plated lead film were flattened and elongated in the direction of sliding by

plastic deformation, revealing a burnished appearance. Figure 15(a) presents a typical wear track on a 0.35-

mm-thick, ion-plated lead film over which a 440C stainless steel ball has passed in dry nitrogen. The wear

track on the 0.35-mm-thick film was similar to that on the 0.55-mm-thick film.

The wear scar on the counterpart 440C stainless steel ball (figs. 14(b) and 15(b)) contained transferred

lead plates and particles. In addition to the small wear debris, plate-like lead debris was found at the edges of

the film wear track. Severe plastic deformation and shearing occurred in the lead film during sliding.

CONCLUSIONS

To evaluate commercially developed solid film lubricants for aerospace bearing applications, unidirectional sliding friction experiments were conducted with ion-plated lead films in 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 lead 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. Ion-plated lead films met both criteria only in ultrahigh vacuum, failing in humid air and in dry nitrogen,

where the coefficients of friction were greater than the criterion of 0.3. Both the lead film wear rate and

the ball wear rate met that criterion in all three environments.
NASA/TM—2000-209088/PART2 5

2. Adhesion and plastic deformation played important roles in the sliding friction and wear of the ion-plated

lead films in contact with 440C stainless steel balls in all three environments. All sliding involved adhesive transfer of materials: transfer of lead wear debris to the counterpart 440C stainless steel and transfer

of 440C stainless steel wear debris to the counterpart lead film.

REFERENCES

1. Clauss, F.J.: Solid Lubricants and Self-Lubricating Solids. Academic Press, New York, NY, 1972.

2. Lancaster, J.K.: Solid Lubricants. CRC Handbook of Lubrication, Vol. II, E.R. Booser, ed., CRC Press,

Boca Raton, FL, 1984, pp. 269–290.

3. Todd, M.J.; and Bentall, R.H.: Lead Film Lubrication in Vacuum. Proceedings of the ASLE 2nd International Conference on Solid Lubrication, SP–6, 1978, pp. 148–157.

4. Lince, J.R.; and Fleischauer, P.D.: Solid Lubrication for Spacecraft Mechanisms. Aerospace Corp. Report

No. TR–97(8565)–4, 1997.

5. Roberts, E.W.: Thin Solid-Lubricant Films in Space. Flight-Vehicle Materials, Structures, and Dynamics,

Vol. 4, R.L. Fusaro and J.D. Achenbach, eds., ASME, New York, NY, 1993, pp. 113–132.

6. Jost, H.P.: TribologyæOrigin and Future. Wear, vol. 136, 1990, pp. 1–17.

7. Fusaro, R.L.: Lubrication of Space Systems. NASA TM–106392, 1994.

8. Miyoshi, K. et al.: Friction and Wear Properties of Selected Solid Lubricating Films. Part 1: Bonded and

Magnetron-Sputtered Molybdenum Disulfide and Ion-Plated Silver Films. NASA/TMæ1999-209088/Part 1,

1999.

TABLE I.—CHARACTERISTICS

OF SELECTED SOLID

LUBRICATING FILMS

[Substrate material, 440C stainless

steel; film, ion-plated lead.]

Film

thickness,

mm

Surface roughness of

films,

Ra,

nm

Mean Standard

deviation

0.55

0.35

98

40

15

9.5
NASA/TM—2000-209088/PART2 6

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

RATE FOR ION-PLATED LEAD FILMS IN SLIDING CONTACT

WITH 440C STAINLESS STEEL BALLS

Film

thickness,

mm

Environment Steady-state

coefficient of

friction

Film wear

(endurance)

lifea

Film wear

rate,

mm3

/N◊m

Ball wear

rate,

mm3/N◊m

0.55 Vacuum

Air

Nitrogen

0.15

0.39

0.48

30 294

82

1530

1.5¥10-6

3.7¥10-6

9.1¥10-6

7.6¥10-7

3.6¥10-7

3.4¥10-6

 0.35 Vacuum

Air

Nitrogen

0.23

0.38

0.42

21 825

115

693

1.0¥10-6

1.7¥10-6

1.2¥10-6

8.4¥10-6

4.0¥10-6

6.1¥10-6

a

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

friction rose to 0.3.

Figure 1.—Pin-on-disk tribometer in vacuum chamber and conditions of unidirectional, pin-on-disk, sliding

 friction experiments.

Load, N (g)

Mean Hertzian contact pressure, GPa

Maximum Hertzian contact pressure, GPa

Ball specimen

Sliding velocity, m/s

Environments

5.9 (600)

0.79

1.2

6-mm-diameter 440C stainless steel ball

0.2

R J C

Ball or pin

specimen

Friction

force

sensor

Detail

Disk specimen

Load

Vacuum, 710–7 Pa

Humid air (relative humidity, ~20%)

Dry nitrogen (relative humidity, <1%)
NASA/TM—2000-209088/PART2 7

(a)

(b)

Figure 2.—Friction traces for (a) 0.55-m-thick,

 ion-plated lead film and (b) 0.35-m-thick,

 ion-plated lead film in sliding contact with 

 440C stainless steel balls in ultrahigh vacuum.

0 2 4 6x105

Number of passes

Coefficient of friction

0.4

0.3

0.2

0.1

0

0.4

0.3

0.2

0.1

00 2 4x104

0 2 4 6 8x105

Number of passes

Coefficient of friction

0.4

0.3

0.2

0.1

0

0.4

0.3

0.2

0.1

00 1 2 3x104
NASA/TM—2000-209088/PART2 8

(a)

(b)

Figure 3.—Friction traces for (a) 0.55-m-thick,

 ion-plated lead film and (b) 0.35-m-thick,

 ion-plated lead film in sliding contact with 

 440C stainless steel balls in humid air.

0 6 12 18x104

Number of passes

Coefficient of friction

0.4

0.3

0.2

0.1

0

0.4

0.3

0.2

0.1

00 50 100

0 6 12 18x104

Number of passes

Coefficient of friction

0.4

0.3

0.2

0.1

0

0.4

0.3

0.2

0.1

00 60 120
NASA/TM—2000-209088/PART2 9

(a)

(b)

Figure 4.—Friction traces for (a) 0.55-m-thick,

 ion-plated lead film and (b) 0.35-m-thick,

 ion-plated lead film in sliding contact with 

 440C stainless steel balls in dry nitrogen.

0 2 4 6x105

Number of passes

Coefficient of friction

0.4

0.3

0.2

0.1

0

0.4

0.3

0.2

0.1

00 1 2x103

0 2 4 6 8x105

Number of passes

Coefficient of friction

0.4

0.3

0.2

0.1

0

0.4

0.3

0.2

0.1

00 300 600 900
NASA/TM—2000-209088/PART2 10

Sliding direction

Film wear track Ball wear scar

Figure 5.—Wear tracks produced on ion-plated lead films and wear scars produced on 440C stainless steel balls

 in ultrahigh vacuum. (a) Materials pair of ion-plated lead film (0.55 m thick) and 440C ball at 116 112 passes. 

 (b) Materials pair of ion-plated lead film (0.35 m thick) and 440C ball at 21 825 passes.

100 m

100 m

100 m

100 m

(a)

(b)
NASA/TM—2000-209088/PART2 11

Sliding direction

Film wear track Ball wear scar

Figure 6.—Wear tracks produced on ion-plated lead films and wear scars produced on 440C stainless steel 

 balls in humid air. (a) Materials pair of 0.55-m-thick, ion-plated lead film and 440C ball at 19 526 passes. 

 (b) Materials pair of 0.35-m-thick, ion-plated lead film and 440C ball at 22 003 passes.

100 m

100 m

100 m

100 m

(a)

(b)
NASA/TM—2000-209088/PART2 12

Sliding direction

Film wear track Ball wear scar

Figure 7.—Wear tracks produced on ion-plated lead films and wear scars produced on 440C stainless steel 

 balls in dry nitrogen. (a) Materials pair of 0.55-m-thick, ion-plated lead film and 440C ball at 8916 passes. 

 (b) Materials pair of 0.35-m-thick, ion-plated lead film and 440C ball at 22 001 passes.

100 m

100 m

100 m

100 m

(a)

(b)
NASA/TM—2000-209088/PART2 13

40x103

30

20

10

0

Environment

Number of passes

Figure 8.—Sliding wear life of ion-plated lead films 

 in sliding contact with 440C stainless steel balls in 

 ultrahigh vacuum, in humid air, and in dry nitrogen.

Vacuum Air Nitrogen

0.55

0.35

Film

thickness,

m

30 294

21 825

82 115 1530 693
NASA/TM—2000-209088/PART2 14

10–5

10–6

10–7

Coefficient of friction

(a)

(b)

(c)

Figure 9.—Steady-state (equilibrium) coefficients of 

 friction and wear rates (dimensional wear coeffic-

 ients) for ion-plated lead films and 440C stainless

 steel balls (a) in ultrahigh vacuum, (b) in humid air,

 and (c) in dry nitrogen.

0.55-m-thick lead film

440C ball against 0.55-m-thick lead film

0.35-m-thick lead film

440C ball against 0.35-m-thick lead film

0 0.1 0.2 0.3 0.4 0.5

Coefficient of friction

Wear rate, mm3/N·m

10–5

10–6

10–7

0 0.1 0.2 0.3 0.4 0.5

Coefficient of friction

Wear rate, mm3/N·m

10–5

10–6

10–7

0 0.1 0.2 0.3 0.4 0.5

Wear rate, mm3/N·m
NASA/TM—2000-209088/PART2 15

Figure 10.—Morphology and elemental composition (a) of wear track produced on 0.55-m-thick, ion-plated lead

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

SEM

(b)

10 m

10 m

(a)

EDX

x105

1.0

1.5

0.5

 0

Ck

Ck

Crk

Crk

Fek

Pbm

Pbm

Fek

Counts

1.5 x105

0.5

1.0

 0

Counts

0 2 4 6 8 14 10 12

Energy, keV

0 2 4 6 8 14 10 12

Energy, keV

Pbl

Pbl

Pbl

Pbl
NASA/TM—2000-209088/PART2 16

Figure 11.—Morphology and elemental composition (a) of wear track produced on 0.35-m-thick, ion-plated 

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

SEM

(b)

10 m

10 m

(a)

EDX

x105

1.0

1.5

0.5

 0

Ck

Ck

Crk

Crk

Fek

Pbm

Pbm

Fek Pbl

Pbl

Pbl

Pbl

Counts

8 x104

3

6

7

 0

4

 1

5

 2

Counts

0 2 4 6 8 14 10 12

Energy, keV

0 2 4 6 8 14 10 12

Energy, keV
NASA/TM—2000-209088/PART2 17

Figure 12.—Morphology and elemental composition (a) of wear track produced on 0.55-m-thick, ion-plated 

 lead film and (b) of wear scar produced on 440C stainless steel ball in humid air.

SEM

(b)

10 m

10 m

(a)

EDX

x105

1.0

1.5

0.5

 0

Ck

Ck

Crk

Crk

Fek

Pbm

Pbm

Pbl

Pbl

Pbl

Pbl

Fek

Counts

1.5 x105

0.5

1.0

 0

Counts

0 2 4 6 8 14 10 12

Energy, keV

0 2 4 6 8 14 10 12

Energy, keV
NASA/TM—2000-209088/PART2 18

Figure 13.—Morphology and elemental composition (a) of wear track produced on 0.35-m-thick, ion-plated 

 lead film and (b) of wear scar produced on 440C stainless steel ball in humid air.

SEM

(b)

10 m

10 m

(a)

EDX

x105

1.0

1.5

0.5

 0

Ck

Ck

Crk

Crk

Fek

Pbm

Pbm

Pbl Pbl

Pbl Pbl

Fek

Counts

1.5 x105

0.5

1.0

 0

Counts

0 2 4 6 8 14 10 12

Energy, keV

0 2 4 6 8 14 10 12

Energy, keV
NASA/TM—2000-209088/PART2 19

Figure 14.—Morphology and elemental composition (a) of wear track produced on 0.55-m-thick, ion-plated

 lead film and (b) of wear scar produced on 440C stainless steel ball in dry nitrogen.

SEM

(b)

10 m

10 m

(a)

EDX

Ck

Crk

Fek

Pbm

8 x104

3

6

7

 0

4

 1

5

 2

Counts

0 2 4 6 8 14 10 12

Energy, keV

x105

1.0

1.5

0.5

 0

Ck

Crk

Pbm

Fek Pbl Pbl

Pbl Pbl

Counts

0 2 4 6 8 14 10 12

Energy, keV
NASA/TM—2000-209088/PART2 20

Figure 15.—Morphology and elemental composition (a) of wear track produced on 0.35-m-thick, ion-plated 

 lead film and (b) of wear scar produced on 440C stainless steel ball in dry nitrogen.

SEM

(b)

10 m

10 m

(a)

EDX

Ck

Crk

Fek

Pbm

10 x104

8

 0

4

6

 2

Counts

0 2 4 6 8 14 10 12

Energy, keV

x105

1.0

1.5

0.5

 0

Ck

Crk

Pbm

Fek

Counts

0 2 4 6 8 14 10 12

Energy, keV

Pbl

Pbl

Pbl

Pbl
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NASA TM—2000-209088/

PART 2

E–12082

WU–523–31–13–00

A03

Lubricants

Unclassified -Unlimited

Subject Category: 27 Distribution: Nonstandard

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 5140, (216) 433–6078.

Friction and Wear Properties of Selected Solid Lubricating Films

Part 2: Ion-Plated Lead Films

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

and Kichiro Imagawa

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

examine the friction and wear behavior of ion-plated lead 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 ion-plated

lead films investigated herein resulted from the environmental conditions. The main criteria for judging the performance of the ion-plated

lead 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 ion-plated lead films met both criteria only in ultrahigh vacuum but failed in humid air and in dry nitrogen, where the coefficient of

friction was higher than the criterion. Both the lead film wear rate and the ball wear rate met that criterion in all three environments.

Adhesion and plastic deformation played important roles in the friction and wear of the ion-plated lead films in contact with 440C

stainless steel balls in the three environments. All sliding involved adhesive transfer of materials: transfer of lead wear debris to the

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

26