ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
Table 1. Test matrix.         (a)   (b)  Figure 3. Test gears.  (a) Just prior to testing.  (b) Installed it rig just prior to closing test chamber. Testing was done at a constant brake torque and motor speed. The torque was 6.8 Nm for the gear as  was applied by the brake and measured by torque sensor. The test speed was 80 rpm for the pinion (and  consequently 43.3 rpm for the gear). The power transmitted was 31 watts. The torque was selected to  provide a tooth load intensity (force per unit face width) similar to the tooth load intensity for the  mechanisms of interest. The speed was selected as the maximum speed that did not induce any  significant rig dynamic loading or vibrations as had been determined by previous testing of similar test  gears. Testing for endurance of the coatings typically required durations longer than a working day, and  unattended testing was not attempted. The testing was paused overnight, as needed, with the test  chamber vacuum maintained by continuous operation of the turbopump, and then testing was resumed  the following day.   The test progression was monitored by visual inspection of the tooth surfaces through a viewport, aided  at times by a strobe light to “freeze” the motion. The visual condition was also recorded by digital  photographs illuminated by a short duration flash through a second viewport that provided a view of the  gear teeth (but not of pinion teeth). The test progression was monitored by displays of the sensor data Test NameTest Article  PairingPinion  Serial  NumberGear  Serial  NumberTooth Side  LoadedExposedTotal  Exposure  Time (days)Testing  Order  Sequence MOS2 1-A A No - 1 MOS2 1-B B Yes 10 3 MOS2 2-A A No - 2 MOS2 2-B B Yes 28 6 MOS2 3-A A No - 4 MOS2 3-B B Yes 17 9 MOS2 4-A A No - 5 MOS2 4-B B Yes 17 10 MOS2 5-A A No - 7 MOS2 5-B B No - 8 MOS2 6-A A Yes 77 11 MOS2 6-B B Yes 77 1261 2 3 4 5P1 G3 P5 G4P4 G1 P6 G6 P2 G2 P3 G5 NASA/CP—2018-219887 132
tangent force sensors. For each test, the average film durability was calculated as the average of the  values from each sensor. The results are collected in Table 2. On average the film durability was shorter  for gears exposed to humid air compared to gears with zero exposure. The film durability for gears with  zero exposure ranged from 190,300 to 53,300 pinion revolutions with an average value of 100,200 and a  median value of 83,500 revolutions. The film durability for gears exposed to humid air ranged from 84,700  to 21,000 pinion revolutions with an average value of 64,900 and a median value of 68,800 revolutions.  Using the unexposed-gear film durability as a baseline, the exposure reduced the film durability by 35  percent based on average values or 18 percent based on median values. These reductions in film  durability are similar magnitude compared to the 55 percent to 20 percent range of reductions reported by  Lince, Loewenthal, and Clark [4].  Table 2. Test Results of Film Durability  The film durability values, from the “Average Value” column of Table 2, are plotted as a function of the  duration of exposure to humid air in Figure 5. The plot shows that while as a group the durability was  longest for zero days of exposure, there is no clear trend of rate of reduction with exposure time. The  range of scatter for the film durability for six tests at zero time of exposure is greater than is the difference  between average durability of exposed and unexposed gears.  Figure 5. Film durability as function of time of exposure to humid air. Test NameExposure  (days)Center  DistanceThrust  ForceTangent  ForceAverage  Value * MOS2 1-A 0 52,000 52,000 56,000 53,333 MOS2 2-A 0 59,000 61,000 65,000 61,667 MOS2 3-A 0 207,000 184,000 180,000 190,333 MOS2 4-A 0 86,000 69,000 94,000 83,000 MOS2 5-A 0 125,000 125,000 136,000 128,667 MOS2 5-B 0 83,000 80,000 89,000 84,000 MOS2 1-B 10 21,000 20,000 22,000 21,000 MOS2 2-B 28 69,000 55,000 74,000 66,000 MOS2 3-B 17 59,000 65,000 66,000 63,333 MOS2 4-B 17 81,000 78,000 95,000 84,667 MOS2 6-A 77 84,000 76,000 88,000 82,667 MOS2 6-B 77 70,000 71,000 74,000 71,667 * average value is the average of the 3 colums to the left median = 83,500 median = 68,800 35% 18% percent reductionFilm Durability (pinion revolutions) unexposed group exposed groupaverage = 100,200 average = 64,900 time of exposure to humid air (days)0 20 40 60 80film durability (pinion revolutions)050000100000150000200000 average for unexposed  average for exposed NASA/CP—2018-219887 134
The behaviors of the films were also evaluated by studying photographs, profilometry, and scanning  electron microscope inspections. During initial running of each gear pair, it was noted that the tooth  surface running-in required very few tooth contact cycles. In other words, the tooth surface appearance  changed dramatically, becoming more glossy and reflective in appearance, after only a few revolutions,  and subsequent further visual changes to the tooth surfaces occurred at a very slow and steady rate.  Figure 6 illustrates typical results of how the surface visual appearance changed for the gear teeth during  a test. The first two images from left to right show the teeth prior to any running and then again after only  1 percent of the total running time. The other two images of Fig. 6 show the teeth after 50 percent and  99 percent of the test duration. The last two images show that with further running the visual condition  changes less dramatically over the final 98 percent of running as compared to the first 1 percent of  running durations.   prior to start ~1 percent of test  duration ~50 percent of test  duration ~99 percent of test  duration  Figure 6. Gear teeth surface appearance for different durations of testing  Wear and running-in of pinion teeth were assessed using a stylus profilometer. The teeth were inspected  moving the stylus with a 2-micrometer radius conisphere tip across the face width. Because the mating  gear tooth face width was slightly less than that of the pinion, there were regions of the pinion tooth near  each edge that did not experience contact with the gear. The data were processed to remove a leastsquares linear form, using only the small regions from each edge of the trace that did not experience  contact for the form removal. Traces of teeth prior to test were collected and processed in the same  manner. Typical results of the inspections are provided in Figure 7. The data plots of Figs. 7(a-b) are for  teeth prior to test. The surfaces show some waviness and some peak and valley features, with peak to  valley distances on order of 3 micrometer, similar distance as the requested film thickness. The data plots  of Figs. 7(c-d) are for tested teeth, and there is an overall wear depth of about 2 micrometers. Certain  worn regions are very smooth.   After 77 days of exposure to humid air, small areas of reddish-brown coloration were noted on some  teeth. Figure 8 is an example of the noted colorations. Close study of digital photographs of the pinions  NASA/CP—2018-219887 135
and gears recorded prior to testing revealed that some coloration appeared as early as 17 days after  exposure to humidity. However, not all teeth had such colored spots. For the pinion and gear pair  exposed for 77 days, there was more coloration on the gear than there was on the pinion. Teeth with  colorations were inspected using a scanning electron microscope (SEM). SEM images from a region  having coloration, at three increasing levels of magnification, are provided in Figure 9. The image  orientation has the face width direction in the vertical direction. The vertical lines are topography resulting  from grinding of the teeth. This region inspected by SEM revealed that the colored areas included raised  material above the surrounding surface. The highest magnification image reveals details suggesting a  “growth” pushing aside and/or through the film. Figure 10(a) provides another SEM image of a similar  structure as that of Fig. 9(c), from a slightly different viewpoint. During this inspection, energy-dispersive  spectroscopy (EDS) was done at the four locations as marked on Fig. 10(a). The resulting spectrum of  Fig. 10(b) is typical of all four inspections. The two prominent peaks of the spectrum are associated with  Mo (molybdenum), S (Sulphur), and Fe (iron). It is speculated that iron oxidation was occurring at the  MoS 2 film-substrate interface and progressed to eventually become evident at the surface.  Figure 7. Profilometer inspections of pinion teeth with traces along the face width direction.  (a-b) Prior to test (c-d) After test.  NASA/CP—2018-219887 136
Figure 8. Red-brown coloration noted after 77 days exposure to humid air  (a) (b)  (c) Figure 9. Scanning electron microscope inspections of a region having red-brown coloration at three  increasing levels of magnification. The vertical direction is the face width direction.  (a) (b)  Figure 10. Scanning electron microscope inspection using energy-dispersive spectroscopy.  (a) Regions inspected, per markings. (b) Spectrum for region 1, typical of all four inspections. NASA/CP—2018-219887 137
Study of plots of profilometry inspections of teeth prior to test revealed one inspection with an interesting  topography that suggests a fortuitous tracing over a region such as revealed in the SEM images of  Figs. 9(c) and 10(b). The profilometry data of this inspection, plotted using three different aspect ratios,  are provided in Figure 11. The inspection was of pinon P5, in the face width direction, tooth side “B” that  later was subjected to test MOS2 6B per Table 1. Fig. 11(a) reveals a localized valley feature of about  1.5-micrometer depth but having a prominent peak feature rising above, out of the valley, by about  6 micrometers. Figure 11(b) plotted using aspect-ratio 20:1 shows some details of the shape of the  feature, while Fig. 11(c) illustrates the shape with true aspect ratio. The breadth of this feature is about  1.5 mm.  Figure 11. Profilometer inspection of a tooth after exposure to humidity for 77 days, prior to test. The  same data are plotted using three aspect ratios (500:1, 20:1 and 1:1).  SEM inspection of a tooth of the pinion, after test MOS2 2A per Table 1, revealed a wide variety of  features on the worn tooth surface. An inspection summary is provided in Figure 12. Figs. 12(a) and (b)  can be used to locate the features of Fig. 12(c) showing highly smoothed MoS 2, blistering, and a region of  loss of film thickness that thereby revealed the underlying grinding-line striation topography. The  elongated blister features are aligned with the direction of rolling and sliding. Although the “delaminated”  region of Fig 12(c) might suggest exposure of the steel substrate, the higher magnified image of 12(d)  has appearance of material flowing in the direction of rolling and sliding. EDS inspection near the center  of this region resulted in a spectrum associated with Mo (molybdenum), S (Sulphur), and Fe (iron)  showing that the region did not experience complete loss of all MoS 2 thickness through this region.0 2 4 6 8 10profile height (micrometer)-2-10123456 5.8 6.0 6.2 6.4 6.6-20246aspect ratio 500:1 aspect ratio 20:1 profile location (mm)6.1 6.2 6.3 6.4-200204060 aspect ratio 1:1(a) (b) (c) NASA/CP—2018-219887 138
(d) (e) Figure 12. Scanning electron microscope inspection summary of a pinion tooth after test 2A, no exposure  to humidity prior to testing. (a) Optical image showing location of SEM inspection.  (b) SEM image near tooth tip. (c) SEM image of blistering and delamination of the film. (d) Close up of delaminated region. (e) EDS spectrum taken from the center of the image immediately to left. Summary  The purpose of this work was to study the effect of exposure to humid air on the durability of a  molybdenum disulfide (MoS 2) dry film lubricant applied to spur test gears and subsequently tested in  vacuum environment. MoS 2 was applied by sputtering onto gears made from induction hardened and  ground S45C steel. Twelve gear tests were completed in a vacuum gear rig at constant speed and  torque. For this study, film durability was defined as the initiation of compromise of the MoS 2’s ability to  provide low friction. Test durations were long enough to initiate this compromise. One-half of the gears  tested had zero time exposure to humid air prior to testing. The other half of the gears were exposed to  air of 57 percent relative humidity for exposure durations up to 77 days prior to testing.  On average the film durability was shorter for gears exposed to humid air compared to gears with zero  exposure. The film durability for gears with zero exposure ranged from 190,300 to 53,300 pinion  revolutions with an average value of 100,200 and a median value of 83,500 revolutions. The film  NASA/CP—2018-219887 139
durability for gears exposed to humid air ranged from 84,700 to 21,000 pinion revolutions with an average  value of 64,900 and a median value of 68,800 revolutions. Using the unexposed-gear film durability as a  baseline, the exposure reduced the film durability by 35 percent based on average values or 18 percent  based on median values. These reductions in film durability are similar magnitude compared to the 55  percent to 20 percent range of reductions reported by Lince, Loewenthal, and Clark [4].  The gear teeth had a very glossy appearance after very few revolutions of the gears. After this initial  running-in, further change in the appearance of the teeth was a slow, steady process. Profilometry  revealed that the wear depth at test completion was on the order of the specified MoS 2 film thickness.  Red-brown coloration was noted on some of the teeth that had been exposed to humid air. The colored  regions appeared as soon as 17 days after exposure to humid air. SEM inspections showed that at least  some of these colored areas included material raised above the surrounding MoS 2 film.  Acknowledgements  This research was supported by the NASA Engineering Safety Center (NESC). The experimental work  was done with assistance from Tysen Mulder, NASA Pathways Intern. Dr. Iqbal Shareef was supported  by the NASA GRC Summer Faculty Fellowship Program.  References  1. Gibson, A., et al, “Overview of Design and Validation of the Fine Guidance Sensor Mechanism for JWST”, 15th European Space Mechanisms and Tribology Symposium, vol. 718. 2013 2. Gibson, A. et al, "Life-test Investigation and Status of the NIRISS Dual Wheel Cryogenic Mechanism for JWST." 15th European Space Mechanisms and Tribology Symposium, vol. 718. 2013 3. Aldridge, D, et al, "Cryogenic Motor Enhancement for the NIRISS Instrument on the James Webb Space Telescope." ESA Special Publication, vol. 737. 2015. 4. Lince, J., Loewenthal, S. and Clark, C. “Degradation of Sputter-Deposited Nanocomposite MoS 2 Coatings for NIRCam during Storage in Air”, Proceedings of the 43rd Aerospace Mechanisms Symposium, (May, 2016) pp. 221-234, NASA/CP-2016-219090. 5. Krantz, Timothy, DellaCorte, C. and Dube, M., "Experimental Investigation of Forces Produced by Misaligned Steel Rollers." Proceedings of the 40th Aerospace Mechanisms Symposium, NASA/CP2010-216272. 6. Krantz, T., and Shareef, I., "Wear of Steel and Ti6Al4V Rollers in Vacuum." Proceedings of the 41st Aerospace Mechanisms Symposium, NASA/CP-2012-21763. 7. Dellacorte, C., Krantz, T., and Dube, M., “ISS Solar Array Rotary Joint (SARJ) Bearing Failure and Recovery: Technical and Project Management Lessons Learned”, NASA/TP-2011-217116. 8. Pepper, S., “Research Note-Characterization of the Test Environment of JWST Roller Wear Evaluation at NASA-GRC”, Aug. 1, 2011. NASA/CP—2018-219887 140
Results  MoS 2 Average friction coefficients ( µavg) with standard deviations measured for the three coatings at 30°C and at  100°C are displayed in Figure 1. The three values of µavg at 30°C for steel paired with MoS 2, Sb 2O3/AuMoS 2 and Ti-MoS 2 are 0.19 ± 0.03, 0.21 ± 0.04, and 0.20 ± 0.01, respectively and are statistically equivalent.  Average friction coefficients for the 100°C tests are 0.09 ± 0.01, 0.04 ± 0.00, and 0.09 ± 0.03 for steel paired  with MoS 2, Sb 2O3/Au-MoS 2 and Ti-MoS 2, respectively. Notably, µavg corresponding to the Sb 2O3/Au-MoS 2 pairing is about 50% less than the values obtained for the Ti-MoS 2 and MoS 2 pairings. The low value of µavg for the Sb 2O3/Au-MoS 2 coating has been attributed to thermally driven Ostwald ripening of the Ag and  subsequent diffusion of agglomerated Ag to the Sb 2O3/Au-MoS 2 surface [6].  Wear volumes (V) for the MoS 2 coating and mated steel ball obtained from tests performed at 30°C are  displayed and plotted against Ed in Figure 2 along with optical images of the wear scars generated after  17,000 cycles. Lines in the figures are least square fits of    =  +   (3)  where α is the wear coefficient µm3/J, Ed is the dissipated energy J, and Vo is the offset µm3. The values  of R2 close to unity indicate the goodness of the fits. The wear coefficients for the ball and the MoS 2 coating  were determined to be 772 ± 26 µm3/J and 3282 ± 10 µm3/J, respectively.  Figure 1. Average friction coefficients and standard deviations for the three coatings at 30°C and 100°C  obtained in reciprocating sliding contact with a sliding amplitude of 1 mm, a frequency of 20 Hz, and a  contact stress of 660 MPa.  Wear volumes for the MoS 2 coating and mated steel balls obtained from tests performed at 100°C are  displayed and plotted against Ed in Figure 3 along with optical images of the wear scars generated after  17,000 cycles. The wear coefficients for the ball and the MoS 2 coating for tests performed at 100°C were  determined to be 719 ± 56 µm3/J and 12,832 ± 747 µm3/J, respectively. The 100°C wear coefficient of the  MoS 2 is about four times that associated with the 30°C results.   NASA/CP—2018-219887 143
Figure 2. Wear volumes (V) for the MoS 2 coating and mated steel ball obtained from tests performed at  30°C are plotted against E d along with optical images of the wear scars on the ball and coating generated  after 17,000 cycles. Lines in the figures are least square fits of Eq. 3 to the data.  Figure 3. Wear volumes (V) for the MoS 2 coating and mated steel ball obtained from tests performed at  100°C are plotted against E d along with optical images of the wear scars on the ball and coating generated  after 17,000 cycles. Lines in the figures are least square fits of Eq. 3 to the data.  V= 719(Ed) - 696 R² = 0.92192 02004006008001000120014001600 0 1 2 3 4Wear Volume(microns^3) Dissipated Energy (J)Ball (100C) V = 12832(Ed) - 10377 R² = 0.94177 050001000015000200002500030000 0 1 2 3 4Wear Volume (microns^3) Dissipated Energy (j)MoS2 (100C) NASA/CP—2018-219887 144
test wound up as a transfer film on the ball. This is an indication that the Ti-MoS2 coating formed an effective  VAL during the 30°C test.  Figure 5, Wear volumes (V) for the Sb 2O3/Au-MoS 2 coating and mated steel ball obtained from tests  performed at 100°C are plotted against E d along with optical images of the wear scars on the ball and  coating generated after 17,000 cycles. Lines in the figures are least square fits of Eq. 3 to the data.  Figure 6, Wear volumes (V) for the Ti-MoS 2 coating and mated steel ball obtained from tests performed at  30°C are plotted against E d along with optical images of the wear scars on the ball and coating generated  after 17,000 cycles. Lines in the figures are least square fits of Eq. 3 to the data. V = 2187(Ed) - 637 R² = 0.99707 05001000150020002500 0 0.2 0.4 0.6 0.8 1 1.2 1.4Wear Volume (microns^3) Dissipated Energy (J)Ball (100C) V= 5032(Ed) + 1357 R² = 0.92336 010002000300040005000600070008000 0 0.2 0.4 0.6 0.8 1 1.2 1.4Wear Volume (microns^3) Dissipated Energy (j)Sb2O3/Au-MoS2 (100C) V = 290(Ed) + 228 R² = 0.6943 020040060080010001200 0 1 2 3 4Wear Volume (microns^3) Dissipated Energy (J)Ball (30C) V = 10816(Ed) - 7672 R² = 0.91732 0500010000150002000025000 0 1 2 3 4Wear Volume (microns^3) Dissipated Energy (j)Ti-MoS2 (30C) NASA/CP—2018-219887 146
Table 1: Wear rates in [mm3/J] determined for the mated ball and coatings tested  at 30°C and 100°C.  Coating 30°C 100°C  Ball Wear  [µm3/J] Coating Wear  [µm3/J] Ball Wear  [µm3/J] Coating Wear  [µm3/J]  MoS 2 772 ± 326 3,282 ± 10 719 ± 56 12,832 ± 747  Sb2O3/Au-MoS 2 17,007 ± 2,939 4,233 ± 194 2,187 ± 6 5,032 ± 386  Ti-MoS 2 290 ± 89 10,816 ± 894 1,438 ± 16 7,941 ± 222  Conclusions  Some aerospace applications such as rolling element bearings and gears have utilized MoS 2 and  Sb2O3/Au-MoS 2 solid lubricant coatings in demanding environments where conventional oils or greases are  unsuitable. Results of this study combined with the results of previous studies [4,9,12], strongly indicate  that Ti-MoS 2 merits consideration as a solid lubricant coating for rolling element bearing and gearing  applications. Important findings of this study include:  •Whereas the MoS2 coating performed well at 30°C, it experienced a high wear rate at 100°C and failed to form a VAL in the contact with a steel counterface. •The Sb 2O3/Au-MoS 2 coating required an elevated temperature of 100°C to form a VAL, and was extremely abrasive to the steel counterface at 30°C. •The Ti-MoS2 coating formed effective VALs at 30°C and 100°C. Acknowledgements  The authors are thankful to The Timken Company for providing financial support and guidance for this  project. The authors appreciate the help of Dr. Barbara Fowler of Timken Engineered Surface Laboratories  for her help in tribological testing and characterization analysis, and Haifeng Qin (UA Chemical and  Biomolecular Engineering) and Zhencheng Ren (UA Mechanical Engineering) for their assistance with the  deposition system. The authors also thank Dr. Ryan Evans from The Timken Company, Dr. Hamidreza  Mohseni (now at Bosch) and Prof. Thomas Scharf at the University of North Texas for past contributions. References  1. Teer, D. G. "New solid lubricant coatings." Wear  251.1-12 (2001): 1068-1074. 2. Hilton, Michael R., et al. "Structural and tribological studies of MoS 2 solid lubricant films having tailored metal-multilayer nanostructures." Surface and Coatings Technology  53.1 (1992): 13-23. 3. Sliney, Harold E. "Solid lubricant materials for high temperatures—a review." Tribology International 15.5 (1982): 303-315. 4. Singh, H., et al. "Tribological performance and coating characteristics of sputter-Deposited Ti-Doped MoS 2 in rolling and sliding contact." Tribology Transactions  58.5 (2015): 767-777. 5. Singer, I. L., et al. "Role of third bodies in friction and wear of protective coatings." Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films  21.5 (2003): S232-S240. 6. Scharf, T. W., P. G. Kotula, and S. V. Prasad. "Friction and wear mechanisms in MoS2/Sb 2O3/Au nanocomposite coatings." Acta Materialia 58.12 (2010): 4100-4109. NASA/CP—2018-219887 148